It doesn't appear to be a trapeze harness, I think it's a safety harness that you tether to the lifelines on an offshore boat. No butt support or trapeze connection.
We have self inflating PFDs, along with regular PFDs. We only use the self inflators on pretty calm weather days. When we first got them, we dumped and they inflated. They do that really well!
But then you have inflated PFDs for the rest of your sailing day. I don't think it's practical to reset them when we're out on the boat. I wouldn't wear one if I were trapping out, I've ended up in the water too many times during that activity!