If you want a fair review, here is mine
It is a good idea, the combining, but in this form it is too bulky and would be hard to use as a knife...if you ever actually "needed" a knife.
About the only reason most divers would ever really have to have a knife, would be entanglement with fishing line or other mono-filament....The knife needs to be kept in a place either hand can get to( in the case of entanglement), and quickly. It should not be some huge bowie knife type hog sticker, it should be small and razor sharp for the emergency use it is intended for....See
BC System Accessories | Halcyon Dive Systems this is worn right in the front of the crotch strap, where either hand can instantly get to it, and even if an arm gets tangled, you have a good shot at getting to this....
Make a knife "similar to this", with a few LEDs on the guard where the blade comes in to the handle....so you will have an emergency light that you can in fact see with, that is slim and great for the only life threatening emergencies you need a knife for...This would sell big I think!
If you really want a good primary light ( the suggestion of your knife in it's present form with the 3 flashlights on it), it should be a "canister light" with a goodman handle so you remain hands free ( and with the cannister, you have a huge duaration of light possible) , or you rig a standard primary light up with a goodman handle, a DIY approach, so you can have the effective use of both hands while lighting your way, without the multi-hundered dollar expense of an ideal cannister ligght ( such as this
Lighting Systems | Halcyon Dive Systems ) ...You could offer a "goodman adaptor" that people could use with many lights, and this could be a great seller!