I have no personal experience with one of those, but when they first came out, alot of the barrel racing people we knew tried them. They didn't like them and most of them went back to a regular saddle. If I understood them correctly their complaint about them was they did not hold their shape good and so would cause soreness in places on the horse. Like I said that is hear say so take it for what it is worth.
Becky
I was just talking to a friend of mine on the phone who sells Amish made saddles over the internet and she just said pretty much the same thing. There is now a "flex-tree" that alot of saddle makers are using that sounds pretty interesting. If you to go www.dixielandgaitedsaddles.com, then click on the Flex Tree Info link, you can read about it. It sounds like a good compromise between treeless and rigid trees. They have some pretty saddles to look at too.