This laser does not light matches until you use a lens, and then it takes a bit of time. But if you want a cheap waterproof laser and I'm sure someone who does aquatic photography of fish etc. Then using this to lure fish etc from there lairs to photograph them, well this will be good to use.
I'm going to take this to a local swimming pool and do a pressure test on this unit. I would guess that 10-30 meters would be it's limit from the feel of it's engineering. But if it survives the pool test then I'd be happy. The pool here is about 5 meters deep which is most peoples snorkeling range whilst on holidays anyway....