It didn't occur to me that we weren't using pfd's in those photos until you mentioned it. We swimming/paddleboarding, around the boat. I would imagine the laws state you wear one, and that's a good idea(certainly in cold water like ours). There may be some state differences and gray areas.

I see a danger in heading downwind a bit, and getting taken out to sea. Same danger we face in dinghies, but kids and new people rarely are aware of that danger that overcomes small boats.