Having fun isn't necessarily stupid. Having fun with flamboyantly dangerous things isn't necessarily stupid. It's endangering unwilling bystanders that's stupid.
Some people like to build and shoot powerful crossbows, or even replicas of medieval siege weapons. These are extremely dangerous and useless things. The dangerous power of a trebuchet to throw an upright piano 150 yards is part of the charm.
But a trebuchet is something that takes certain amount of thought and sacrifice to obtain and use. This flamethrower thing is more like a powerful handgun. There's been a recent fad for ridiculously overpowered handguns, which pack superfluously fatal power into a convenient, affordable form factor. The recent brouhaha over "armor piercing" ammunition was a side effect of a manufacturer selling a cut-down semi-automatic carbine as a "handgun", even though if you look at videos of people using them they're obviously terrible as handguns. This raised the question of whether 5.56 NATO ammunition should be regulated as "handgun ammunition", and in the end I think the decision not to was reasonablee. These aren't cop-killing or military handguns. They're extremely dangerous toys designed to get your rocks off.
There are some who'd say that because these guns are dangerous and impractical they should be banned. But I don't agree. "Impractical" isn't the same as "useless" because getting your rocks off is a legitimate use for a thing. I think people should be able to enjoy their ridiculous firearms as long as they do it at some kind of appropriate range. I also think there's a real danger though from stupid people who will go plinking in the woods with the things like they were BB guns.
That's really the only problem I have with this flamethrower, whether it's gold, chrome, or gunmetal gray. Any idiot can buy one, but it'd take someone reasonably intelligent and determined to find a place where it can be used safely. I'm not against people buying them, but I am for coming down hard on people who use them where they're a danger or public nuisance.