This gun makes a loud pop when fired and will surprise anyone nearby.
Depending on the air pressure this gun can be a safe prank or a powerful air gun that is dangerous. A safe pressure to play a prank would be anywhere from 10-20 psi, but as a gun this should be fired at NO greater then 45 psi . At 70 psi or greater you are in danger of having the bottle explode and that would not be very pleasant.
This is a really fun project and the videos don't due it justice.
You really have to try it out to understand, and besides it is free and easy!