The beach club is the same beach as the public beach. The beach is nice, but not amazing and there is drink service. I stayed for five nights in September and the whole beach mood was pretty subdued and not crazy or noisy, but I am unsure of what it may be like at other times throughout the year.

Before using the beach club across the street my wife and I decided to check out the (free) public beach that is just a minute walk across la croisette (directly next to the beach club). After spending one morning there we decided to not even try the beach club. We spent at least part of everyday at the beach, which was perfectly clean and uncrowded. There are no chairs or shade, so if that is a non-starter for you the public beach won't be a good option.

I can't speak to other Marriott French beaches or other times of year, but I was very concerned I was making a poor decision prior to the stay, but it ended up being perfect for what we wanted (a relaxed beach time after 10 days of site seeing in cities).