While it looks like something an insurgent might carry, it is relatively harmless (unless it hits you in the face), it fires 1.5L soda bottles partially filled with water up to 115 feet (35 meters) when it is held at the optimal angle (35 degrees). Marudai says to expect recoil – lots of it.
Needless to say, this should probably be kept out of the hands of children – and given the price it will probably stay out of the hands of children because the only thing that hurts more than getting shot in the face by one of these things is paying $361 plus shipping (from Japan) for it.
Price: ¥28, 350 (~$361 USD) Caveat emptor: while there are ways to import stuff from Japan, you might have trouble with customs – whether bottle rocket launchers are subject to import restrictions or not. [Source]