I love keychain tools, I have quite a bundle in my pocket, so much so that I don't even keep my KEYS on my keychain. One thing I like is to carry a blade to add to my utility, so having a safe, secure and stealthy cutter like the Gerber Daily Carry Hook Knife really adds to my lifesaving potential, in the form of a reliable, easily stowed in my pocket. I added this to my keychain of mini tools, and it's been a very useful addition.
Gerber's idea behind the stainless steel hook blade is simple; it's an ultra-stealthy cutting tool that lives stealthily on a keychain and can be quickly deployed to quickly cut yourself out of a piece of clothing, seatbelt or other safety strap, or do the same for a loved one, or a battle buddy, if you should you ever find yourself in a rough spot. I've also found a number of day to day uses for the little knife. There are plenty of other ways to use a safety knife on a ring. 
Using the ring at home, I put it to use opening boxes of goodies and dreaded utility bills. I cut ribbon, opened snack-packs and trimmed tags out of clothes. Out bush I've used it for cutting costs and fishing line, and opened up vacuum sealed food. I even used it to cut long grass for some little weaving craft jobs I was showing off to Tactical Baby and Triceratops Girl with. 
At just over 2" long, it's innocuous and barely stands out on my keychain, the cutting edge is secured neatly in the hook, which in turn is stowed away in a small hard nylon friction lock scabbard, with a keychain loop to secure it. I gave one to each of my partners for Giftmas, and they went directly into handbags. One reported that they often found the blade loose in the bag, having come unstuck from its scabbard. A little alarming, but more from a loss perspective rather than risk of accidentally cutting things. 
The ring is copper lined, which is a nice accent, and go feels good around the finger, and there are rounded crenellations on the back to give a good thumb lock on it when you are getting ready to do the cutting. The angles all work nicely to allow you to put some real power into the cut. My favourite test materials of paracord and cable-ties, neither of which offered much trouble, singly but due to the small size of the ring and its hook, you wouldn't want to load it up as heavily as you might with a full size rescue hook like the Gerber Crisis Hook. It's easily comparable in cutting power with the Benchmade Figure 5 Cutter Since it's a pocket sized tool, I don't expect it to be for heavy use, rather for "I just need to cut this little thing, but right now" moments, especially if they are in delicate situations.
