What's good about this knife
Wide Hilt
The knife has a wide, contoured hilt, protecting your wet hands from slipping down over the blade.
Wet grip handle
The knife has a handle which stays grippy in the water.
Serrated blade
A knife is an essential safety tool for freedivers. This knife's serrated edge cuts easily through fishing lines and ropes.
Rubber loop closure
You are never in doubt whether you have re-sheathed this knife correctly. Some knives have invisible locking mechanisms, but it is hard to hear the "click" of such a mechanism in the ocean through a wetsuit hood, so a visible locking mechanism like this knife's rubber loop is better.
Calf straps
I recommend wearing your knife on your inner calf so that it doesn't get tangled while swimming through kelp forests. This position also makes it easy to see while wearing a mask & wetsuit, so you can visually verify that you have re-sheathed it correctly.
What to avoid in a knife
Narrow hilt
Don't buy a knife with a minimal hilt. Without a hilt, if you are pushing against something, it is easy for your cold wet hands to slide down over the blade.
Paracord handle
On land, paracord is a useful survival item, and makes for a grippy handle, but in the water it loses its grip, making the handle slippery. Choose a knife with a hard rubber or metal handle instead.
Invisible locking mechanism
Some knives click back into their sheath with a "click". On land, it is easy to hear this "click", but not so easy in the water with a hood on. This makes it easy to mis-sheath your knife. Get a locking mechanism you can see.