Everybody that dives should have a Rescue clipped to their BC - IMO the perfect blade design and construction for a SCUBA EDC.
My current U/W "EDC" is an orange Zytel Rescue in ATS55, but I used a plastic clipped, zytel Rescue in AUS8 for several years. I attach them to my BC with a stainless split ring through the lanyard hole, clipped to a fastex buckled connector, attached to my BC.
Both steels exhibit rust quickly if not attended to, but in my experience it doesn't affect performance, and most importantly, can be prevented fairly easily.
Both my 440A Gerber Patriot, and my Rescue(s) get a (very)light coat of CLP/BreakFree before each day of diving. As soon as I exit the water following a dive, I try to rinse the knives in fresh water, if not on the boat then as soon as I can get to a hose/rinse tank.
The combination of CLP and frequent rinsing does a good job of preventing rust, and any rust that may form is typically on the exposed part of the blade, and not the edge, as the edge is more protected from airflow. It's also fairly easily removed -although my AUS8 knife has some discoloration after probably 50-60 hours total underwater in ocean environments, it's perfectly serviceable and now serves as a garage utility knife.
No better knife for cutting monofilament or any kind of rope - easy to open with gloves, strong lock - a great SCUBA folder.
