Just responded to you question on another board. But in case you don't see it....
we have used them a couple times. One was for the Sheraton Vistana Villages and the other was at the Marriott Grande Vista. Never had a problem with them.
We've been renting the last 2 years from timeshare owners so it's been a while, but I do know they are legit and have never heard of any problems with them.
Hope this helps!