I have seen them at the tack shop, but I don't know anyone who actually owns one. They seem interesting, and more comfortable than two bars, even well padded bars. They seem like they'd be good for a tough-to-fit horse, and would be close contact too.
I wonder if they are secure enough... My instinct looking at them was that they were sortof like a bareback pad with cantles and stirrups... I wonder if they would stay in place in a slippy situation without the tree... kindof like the risk with bareback pads that have stirrups.
The only people I've talked to that have used those saddles didn't like them. I don't remember why but I'm thinking it's what you said, it feels too much like a bareback pad with stirrups. I almost always use a bareback pad but I would never try to use it with stirrups, too dangerous.