What a luxurious experience.
The boat we were on was Mon Cheri 2, which was apparently their newest boat, built in 2019, and it shows. The cabins are spacious with a bed that could have fit 4 of me, and a huge picture window and spacious balcony. Plenty of closet space, even a little desk for writing. AC was very new and very strong.
Bathroom was nicely sized, with a shower on one side (great water pressure, instant hot water), and a Jacuzzi on the other (unfortunately, mine didn't work, but the staff offered to fix it, and it wasnt a big deal for me). No need to bring anything - they have dental kit, comb, you name it.
I did the 2 night stay, which I recommend, since it allows you some more time in the region when there's fewer guests around. First day was kayaking near the boat. Second day was a bike tour on Cat Ba Island (very sweaty but lovely to get out and about), then some more kayaking. Third day was a cave trek (didn't join). Second day, we were transferred to a day boat, which was still very nice with AC and the full spread of lunch just like on the main boat.
The staff was warm and welcoming, though the onboarding was a bit hectic with a bunch of boats boarding one after another. The staff all address you by name during the experience, and are generally very observant and consistently offer great service for anything you need.
I added on a very nice massage which solved my back problems for a bit.
The pricing for extras (drinks, for instance) will be higher than what you see elsewhere in Vietnam. Just forewarning.
All in all, 10/10 would travel again, and would bring my family too!