Padi Divemaster here (200+ logged dives). What are you going to use it for?
1. Line cutting? - Get a scissor or a line cutter (I use an eezycut trilobite).
2. Killing fish? - Get an UV hunting knife (ceramic or titanium)
3. To have an all-round tool? - Get a medium length titanium knife, with line cutter and a part of the edge that's serrated.
If you are diving in waters where there is a possibillity that you might get caught in a fish net or something similar. I would advise you to allways have TWO tools for line cutting. One is to be easily reached by your right hand (e.g. Inflator hose) and the other by your left hand (e.g. right leg, on the inside of the calf, NOT the outside).
Sorry for grammar mistakes should there be any. English is not my first language.
