Had one for the last year or so. Relevant to my line of work and whilst i have a laptop and gear that can do everything it can do and better figured it was worth a punt on the kickstarter at the time as i'm a sucker for a good gadget.
Usage wise, it's a cool little toy and it can do a number of useful things. Most useful for me so far has been:
Clone a mates hotel key so I could dump my bag in his room and get it later. - This is a ridiculous use case, but it was rather handy.
It's brilliant for presentations - by far my most common use, the bluetooth acting as a controller for powerpoint.
Changing sources and controlling my father's TV when neither one of us could be arsed to get up to get the remote controller after settling down to watch a movie.
Oh and annoy my sister by setting off her doorbell.
Haven't used it in anger on any red or pentest jobs as it just hasn't been required or when I have needed something it could do, I've had better equipment on me at the time (e.g. a proxmark).