There were some postings about this last week--you might try a search. Basically, from what I understand, the answer is yes, you can save money with them and they are legit.
I personally had a bit of a problem when I tried to book with them for a busy WDW week---most of the listings were "upon request" which means they don't have the room unless the hotel gives it to them. The hotel I tried to book was not available in the end, what they offered to substitute it with was no where near comparable (and they wouldn't even guarantee me the rate up front) and they took 5 full days (including a weekend) to get back to me instead of the promised 48 hours. My cc was never charged though.
If you can book a room with them that says "room available" you should be fine though.
HTH