Henry had already thought it through. According to him, currently, just from the fact that they were currently managing to get things that could increase their strength, it implied that they could be found within this world.
Since that was the case, it was clear that there were people that were stronger than them. And in case by bad luck they somehow met with one of them, and that person decided to attack them, then they would be in trouble.
They did not have to use all the money that they currently possessed in order to purchase the next item that cost $1 billion, considering that they would have to make some investments.
But still, they could purchase one of them, and have one person take it. With that, they would at least have someone of that strength after the improvement, who might be able to deal with a problem in case it suddenly appeared.
