I once hosted one of these sessions, for about 20 people, as part of a larger safety conference. We worked with the hotel that was hosting the conference, closed their swimming pool to the public for an hour, and all jumped in with our inflateable pfds and fully clothed. (That POP! when the inflateable goes off is startling, the first time).
One of the other hotel guests reported us to security - "There's a bunch of drunks swimming in the pool with their clothes on!"
Seriously, knowing that your pfd will support you is something that's useful to try once. After that, use a jackline or whatever it takes to keep yourself on the boat.