We've used this kind for five years
Our youngest started sailing life at 1 week, and as soon as she was mobile she was in one of these. I like the design because you pick them up and carry them using the handle at the back. Plus the collar ensures they'll float head-up, and be cushioned from any knocks.
When we were sailing (6 knots yawn), we rigged a safety line so the toddlers could move up and down the deck.
On the rib, I've taken the view that being attached is pretty dangerous, so we use the jackets above, and sit them on the lap of an adult on the bench seat - and watch the speed.
This summer, number 4 will be born (oh boy), and we've never had a rib + one so young. Has anyone managed to do any ribbing with one so tiny? I'm thinking car seat on deck, flat conditions and 25 knots max.
Before anyone shoots me down for something so reckless, consider that a Scorpion in flat seas is a safer place to be than the M25 ...