Love 'em. I even have several french cuff shirts that I bought as a present to myself when I gradutated college. They're even monogramed. I think I've worn them twice (that means at least 3 of the 5 have never been worn in the last 4 years of owning them).
Cool idea. It would even be better if they made them out of motorcycle chain links - bigger and less likely to slip through the holes in the cuffs.
Those could get expensive. If I bought a pair I'd have to buy a french cuff shirt to wear with them. Then I'd have to buy a new suit to wear with the shirt. I can't remember the last time that I wore a sport coat and tie, I think that it's when my niece got married but I can't remember how long ago that was.