Sailed with a friend on this winter sailing round the Med from Barcelona, and can't recommend MSC Yacht Club experience enough.
From the moment you arrive and make your self know to any of the butlers, you will have the most beautiful time, MSC beat any other cruise line, hands down with the attention to detail and service for YC guests.
We booked a YC Grand Suite, which was originally just a slightly larger YC Balcony cabin, but they rebadged it to a GS, so it is just a larger version of the balcony, not much else to distinguish it being a GS. We knew this before booking so it more than met our expectations.
Usual well appointed YC cabin with the most comfortable bed on a cruise ship you will get.