I've done these before, and don't see any problem as long as you are sure that you will be there. There isn't much ambiguity when you book them. They state pretty clearly that you will be charged up front, and that they are non-cancelable, non-refundable. It's not like they try to hide this in small print to trick poor unsuspecting travelers into their evil clutches.

Also, I usually save more than $10 when I do them. IIRC, when I have done it, I have saved more like $30-40.