Dealing with Horcruxes had become second nature with Voldemort's memories and his practical experience. There was no drawn-out mental battle, just a quick overpowered attack and a full format of the soul piece holodisk before it was cut up and stored, ready to be consumed at his convenience.
After being fully energised by the Voldemort soul cookie he ate, Harry spent the rest of the night studying the Diadem. Even with the few memories he had regarding runes, he was no closer to figuring out how it was constructed or what it did when Boppy informed him of the completion of their task hours later. There was no way he was going to just plonk a potentially mind-altering artifact on his head to find out. That was why he had thug/criminal test subjects.
Unfortunately, he would have to wait a while before he could test it, as a few children that suddenly became retarded overnight would probably be noticed by the Professors. Harry doubted it would be as great as the rumours though, and while he was very interested in it, he found it easy to wait instead of just testing it out on himself.
Only an idiot would do that, much like an SI putting on the Sorting Hat because he had read in fanfiction that there were rules to stop it spilling any secrets it uncovered. Or simply making the wearer braindead from some self-defence trigger or something. That took a lot of bravery or a lot of stupidity. Which one or if they were the same thing was debatable.
With the elves having cleared everything out, Harry gave up on the Diadem and gave it to Boppy to store at the Godric's Hollow base. It was now time to find out the rules of the room so he could take full advantage of it. He had already long ago had his elves move any of the spying portraits within sight of the main entrance to the place. After testing, the secret passage to Hog's Head Inn was revealed and the perfect escape route, other than Vanishing Cabinets, was found.
Unlike how the book portrayed the tunnel, it was not in fact made by the magic of the RoR. If any magic was involved at all, it was revealing the entrance at both ends of the tunnel as Aberforth Dumbledore had no idea it was there and had covered it with a portrait of his sister. If the room had somehow magically created a permanent passageway, it would have been a massive security risk if a spy found the RoR.
The spy would be able to make a permanent path to nearly any place within Hogwarts or the surrounding area. From the Headmaster's guarded office to the Chamber of Secrets. Harry had in fact tested this as soon as he thought of it, only to be disappointed that J.K Rowling had misled him with the unlimited potential of the place. He had expected to be able to use the room as a key to anywhere and create whatever he needed.
The room was thought to have some degree of sentience because it transforms itself into whatever the witch or wizard needed it to be at that particular moment in time, although there are some limitations. To be able to read a person's thoughts and then magically model a room to specific needs was nothing short of astounding.
So far, he found that it could magically create anything the 'host' imagined, but it could either not leave the room if it was too complicated or disappear once outside within an hour if it was basic like cleaning supplies. Magical or complicated items would also not work like the original when created. Much to his further disappointment, the computer and Philosopher's Stone he created merely looked like the originals but were basically just movie props.
It created the same exact make and model laptop he imagined, but it failed to turn on or work. When he smashed it apart to check inside, it looked like propper components at first, only to reveal incomplete circuit boards and hard drives. Maybe if he had complete intimate knowledge of the creation of the computer, he could get it to work. It was the same for books he had never read or materials he didn't know the exact composition of.
One of the first substances he had tried to create was black powder and gun powder, only to find it looked and smelt like the real thing, yet did not combust. This disproved his theory about creating anything if you knew it intimately. Harry had researched gunpowder when reading historical self-insert novels to see how full of sh*t the authors were when a random keyboard warrior was able to make it like it was nothing special.
This meant that the room was basically just a Hollywood movie set that could create any prop needed. You also had to be very specific about what you wanted the place for, as it would permit other people to enter the room while it was already being used unless indicated. This was tested with Boppy trying to enter when Harry had created a training room. However, this could easily be negated by the overpowered house-elves simply by teleporting directly into the room if the door did not appear for them.
It could not summon real items like the Hufflepuff Cup or the Sorting Hat. Harry even tried summoning and producing real gold only for the first to not work and for the second to disappear in an hour. There was no time-travel or time dilation within the room. It couldn't even duplicate his wand to create a permanent backup. Overall, Harry was quite disappointed with the RoR.
It was still a fantastic magical marvel, but fanfiction had filled his head full of game-breaking ideas only to be given a healthy dose of reality when he finally got around to testing it. Harry should have known better, if it was really as powerful as he believed, Draco could have used it to just fix the broken Vanishing Cabinet or make a new one. He would have certainly been thinking about it. The RoR was basically limited to whatever a wizard or witch could do with a wand.
Luckily, it also cleaned up anything left in the created room as otherwise, Dumbledore's sh*t would still be in a magically created chamber pot after he stumbled across the room when he needed a toilet all those years ago. There was one use, however, that Harry would be taking advantage of. The RoR was capable of recreating any book that had passed within the castle's walls. Any book that had been placed in the restricted section or removed by the Ministry would be able to be produced.
This still meant that he would need to buy up some blank books as Doubling Charm was not permanent and tended to deteriorate quickly after a certain amount of time. The charm was used to duplicate an object, creating an exact replica that was indistinguishable from the original. But it could be dispelled and was not permanent. Thankfully, there were other spells that could transfer text from one book to another, and would not fade if used on a real blank book.
Updating his personal library would keep Boppy and his minions occupied for a while as they copied every book Hogwarts had ever seen. Hopefully, even the Founders' personal journals or spellbooks would be included. Although Harry was capable of casting most spells with imagination and willpower alone, there were always going to be limitations or a more simple way of casting a spell, which was why foci were introduced in the first place. Having some OP wand spells would still be useful to him.
The Fidelius Charm was an excellent example of this. There was very little chance of Harry casting this monster of a spell wandlessly or even solely with a wand. It was more like a ritual than an actual spell. With how much concentration was needed to be applied to all the different aspects of the spell towards multiple targets, using a ritual would take off most of the pressure so the caster could mainly focus on guiding the complicated spell.
Otherwise, he would have to direct, power and concentrate on all the individual processes involved with wiping out the memory of an object or building from multiple people. This would become more and more difficult for the number of victims that knew about the target or would actually see the target and have it continuously removed from their mind so that their eyes didn't register it. It didn't make the target invisible so much as continually erased any visual memory of it.
The Fidelius Charm practically erased something from existence except for a select few that would have the secret engraved in their soul. This was why ritual magic was created in the first place, to mitigate the massive amounts of concentration and energy needed to cast more complicated spells, particularly if it involved modifying the caster's body. It was hard to concentrate when you were in extreme pain.
Unfortunately, the Fidelius couldn't be cast on concepts, only objects or buildings. Otherwise, Harry could set up a huge ritual and cast the charm on the concept of magic itself. Then there would be no need to enslave all the magical idiots to stop themselves from starting a war with muggles. It was also restricted by how many people were aware of the object the charm is cast on. Erasing the memory of the Eiffel Tower, for example, would be virtually impossible.
Harry had thoroughly investigated the charm because it had many applications that would make his life more comfortable. If he could apply it to himself so Dumbledore forgot about him, he would be able to operate with impunity. The same would be for any weapons he used or bases he built. If the enemy didn't know about him, could not find where Harry lived, or see what was killing him, he would stand no chance.
With the functions of the Room of Requirements uncovered, the only benefits he received was an unknown escape route, a room full of junk with hidden treasures, a comprehensive library, and a training area or hideout. It wasn't unexpected, but he would have preferred the room to be more overpowered.
Since several of his plans revolved around some of the now-debunked abilities of the RoR, Harry would have to wait until Christmas to see if the Dark Lord would be stupid enough to hand him the invisibility cloak like in canon.