I once saw someone light up a can of starting fluid (ether) with a $0.79 Bic lighter. 10 foot diameter fireball.
The bad things about carrying a flamethrower are: (1) heavy, (2) bulky, (3) makes you a target, (4) you get fried if the fuel in the tanks gets ignited anywhere but the muzzle of the flame gun, (5) the flame mixture tends to make the operator violently ill, and (6) the heat from the fire (2,200 degrees F) is incredible for the operator. Other than these few drawbacks, flamethrowers are cool. [However, they are unsuited for concealed carry.]