Most flat earthers (those that seemingly seriously believe in that) are just too lazy and, in most cases, too unwilling, to actually do anything to try to prove their assertions. They just make their claims, and they do nothing to corroborate them, or to check the counter-claims. For them it's enough to type furiously at a keyboard and make YouTube videos, and come up with all kinds of often hilarious arguments.
But then there's this small minority of flat earthers who actually do try to prove their claims.
Their problem? The ways they try to do it is usually as stupid as their arguments. Sometimes even dangerously so. At least dangerously to themselves. As in outright suicidal. And, as in the example below, completely unnecessary.
He didn't get himself killed, but he was injured to such an extent that he had to be taken to a hospital with an ambulance.
There are so many stupid things about that whole thing that it's hard to decide where to start.
Firstly, and most obviously, you don't need to launch yourself with a rocket in order to see the Earth from a high altitude! D'oh. The guy is literally surrounded by cameras right there, at the launch site, and he didn't seem to get the idea that "hmm, maybe I could launch a camera instead of myself, so I don't endanger my own life."
Moreover, a camera weights less than 1 kg, rather than the 70 or 80 kg that he does. This means that he could design a rocket to launch it much, much higher with the same amount of fuel.
Thirdly, why use a rocket? Both hot air and helium balloons have existed for a hundred years or so.
Fourthly, and if the argument is that he wants to see it in person, rather than trusting a camera, just using a regular old airplane can get you to an altitude of several tens of kilometers. That 550 meters is just pitiful. And dangerously stupid. Why would anybody think that a rocket would be a better idea than a plane?
Heck, driving up a mountain will get you to a much higher altitude than 550 meters, and you don't even need to do or own anything special to do that, other than a cheap car. There are mountains, with paved roads on them, that go several kilometers high.
Not that getting eg. to 10 km with an airplane is going to convince him (because even at that altitude the curvature of the horizon is still far from obvious, and a plentiful of bias is going to make him deny seeing any such thing; getting to an altitude where the curvature becomes blatantly obvious requires an altitude that's not easily reachable by civilians), but at least it would be a million times safer and smarter than trying to do it with a home-made rocket.