For the boy who wants the ultimate destructive toy, I daresay this comes close.
There's a more in-depth video discussion of this flamethrower here, including the laws and regulations governing their ownership and use (there aren't many of them).
There is a practical application for flamethrowers, of course, in setting fire lines for back-burns, etc.: but they tend to be lower-pressure, shorter-range units. This beast is designed to dump its cargo at maximum range and velocity, as quickly as possible. It appears to have much the same range and burn duration as the US World War II M2 flamethrower.
Despite an extensive history of military flamethrower usage, I wouldn't recommend using it for defensive purposes . . . just imagine what a prosecutor could charge you with if you incinerate your attackers!