I used mine for snorkeling offshore of Grand Cayman in February, and it is a great little knife. Mine's coated with whatever the black stuff is, it show's no rust spots whatsoever. I don't know if it can be had uncoated, but I don't think I'd take it in the drink uncoated. I rinsed it each time in tapwater after saltwater emersion.
The knife is made in Italy, and is of good quality. The blade steel (I was told) is 420 stainless, which is actually a good steel to use when you've got as thick a double-edge as what this knife's got. It made for easier reprofiling to a thinner edge on my Spydie stones. The serrations on either side work pretty well on rope, but aren't the greatest by any means. They too needed reprofiling on the corners of the Spydie stones.
All and all, it is a good underwater knife. I wouldn't consider carrying it on land for any purpose since it's really a single purpose design in my opinion. I got rid of the clip, by the way, and ran velcro straps through each slot to secure to my calf while in the water. Hope this helps.
Professor.