I think they are GREAT for a very short term rental, but I'd never ever ever do it for more than a month, if that.
I've used them twice for quickie laptop rentals, and wouldn't hesitate to do the same for anything else. But that would just be until payday.
I had friends a while back who really got in over their heads with the renta center type places. They practically furnished their house with the stuff and ended up losing most of it because the payments were so high.