But how much buoyancy has this harness?

Are their sizes and buoancy for weight classes?

Is it a swimming vest or a lifesafe vest? I have the the impression that they try to offer both in one vest.
That's impossible: I have a life vest which keep my head above the water if I'm unconsious. So the foam (which is only on my chest !) is 7 cm thick. And left 2 cm thicker as right for turning me up if miy face is down.

The danger with these type of gear is that it is only for show.