I buy it before every Divina cruise. Feels more like it's free\included in the cruise when I've paid for it well ahead of time. 🙂 There is no difference in price between on board and beforehand so you can wait but I like having it done not having to spend the time going to the F1\4D theater to sign up.
It does include everyone in your cabin and all 3 (F1, 4D, and Bowling) are unlimited use. Mostly we use it for the bowling and will maybe do one or two movies and one or two spins with the F1 but mostly it's the bowling. I have almost never seen both alleys working for a full cruise but usually one will be.
Do check your bill after a day or two though. A couple of cruises they billed me for each string of bowling but a trip to the service desk was all it took for have them removed and the billing fixed for the future ones.