On the topic of diving knives...back many years ago, when I was diving, I chose the blunt tip knife. Most uses for a diving knife are slicing or prying...more use as a utilitarian tool than need for a pointed sticker.
One of the first thing to happen with some divers is they end up breaking the pointed tip right off of their knives.
Blunt Tip Scuba Diving Knives
Also, research the different grades of stainless steel and get a good grade...not all stainless is created equal. In any event, you'll want to rinse everything in a fresh water bath after diving anyhow. Stainless may not rust, per se, but it can corrode somewhat with salt water exposure.