I made one seeing as the total cost was only a few dollars. The first time I shot this I was amazed. The rocket went incredibly high, nosed over and ended up in a tree about 100m downwind. They can also be used in rocket cars, but you must make them less powerful by putting a new blue gasket with only a tiny hole in it to reduce the water flow. (the gaskets you find in the lid of soda bottles)
IMPORTANT: SAND THE CAP BEFORE YOU GLUE IT!!!!!!!!! I have had an unsanded cap blow out and launch the rocket horizontally!

I make my rockets with a balsa wood stick down each side, long enough to reach past the nozzle. I attach the fins to the end of these sticks (these rockets are unstable if you don't make the sticks long enough, because the water is sitting in the back of the rocket, when in a normal rocket the front would be heavier)
I use my launcher as a handheld one, not attached to a stake as they say on the site......when you shoot it you get dreched lol.
Has anyone else made rockets like these??????
EDIT: Look a few posts below this one to see a diagram of the rockets I use.