We went on the Bliss Cruise last year. And yes, it was a fantastic way to meet (and play with) people!
We chose to "pre-meet" people online before the cruise, rather than taking our chances with chance meetings on the ship. That said, we found even total strangers to be friendly and open. We made a point of sitting with people at meals, rather than sitting by ourselves. That was a nice way of introducing ourselves to new people.
There were some existing groups of people who knew each other, but somehow those groups seemed more open, and less "cliqueish" than groups sometimes can be at clubs. We fell into a great group of couples who all seemed to know each other, and they seemed happy to treat us like old friends!
One advantage of the lifestyle cruise setting is that everybody is treating this like a special occasion, and a unique opportunity to play! So I think people are more ready to be friendly, flirty, and playful than in other settings that are more "routine".
Hmm, disadvantages? I'm having some trouble thinking of any. I guess people could find the sheer number of people onboard to be intimidating. But if you try to make contact with some couples beforehand, the numbers seem more manageable. Also, there are so many meet and greets and other social events, making it easier to meet people on an individual basis.
My opinion is this: if you are considering a lifestyle takeover cruise, sign up now! You'll have a great time!