I've seen some pretty cold reception to these devices; their outrageous price being one of the big negatives.
Also, in regards to the cell relay device that Shoctor posted about, they're not all that great either. We used one temporarily in one of our offices until we could get a full strength repeater put in and the little ones that Shoctor posted about can only handle three simultaneous calls. I'm not sure what happens when the fourth call is attempted, but most likely you just don't get through.