My wife, 8 month-old son and I sailed an Eastern Caribbean itinerary in the MSC Seaside Yacht Club.
The Yacht Club is every bit as amazing as all the reviews on here state. I don't know how anyone can give it less than 5 stars. We sailed in the Yacht Club on MSC Divina in 2017 and we have not wanted to cruise with anyone else since because of the Yacht Club. They have made the product even better on the MSC Seaside. The biggest plus being that the Seaside Yacht Club restaurant is actually inside the Yacht Club instead of on the opposite end of the ship such as it was on Divina. We also liked the wristband cruise card replacement.
Embarkation was very smooth with priority check-in and butler assistance from the curbside all the way to the stateroom. It took us about 15 minutes from the arriving at the port to be on the ship in our stateroom. Disembarkation was also as smooth and we were escorted off the ship by our butler at our leisure.