We booked a Condo through 'Jet Luxury resorts' at the Signature for four nights, mainly because of the daily rate was much better than booking directly. I was a bit nervous booking through them due to some of the negative reviews, but I did not experience any of the issues mentioned in other comments: we had clean rooms, plenty of towels for the 4 persons that we booked for, daily housekeeping that was very friendly, same excellent treatment by hotel staff as the people who booked directly with Signature.
Valet parking was free of charge and we were able to use the MGM facilities (pools, lazy river) for no extra costs.