This is another one of those (I admit it, jealousy motivated) some people have way too much money posts. In this instance, the item that prompted this reaction is Fendi's keychain/tape measure because, useful though it may be, how many times do you use a tape measure on a day-to-day basis? Personally I may have a yen to measure something maybe once a month but definitely not with the level of consistency that would induce me to shell out a couple of hundred dollars for the (logo-emblazoned) pleasure.
Seriously, it's cool, but I'd probably wind up snapping the keychain part open by accident all the time, thereby losing all my keys.
So I suppose it could be useful, but I still maintain that I've never met a Fendi bag (or small non-shoe accessory) that I like.