Q: What are your thoughts about treeless saddles?
A: I personally ride in a treeless saddle. It is a very simple one, the Ansur Classic. I love it because I am so close to the horse. I also love it because there is no way it will ever restrict or bind or bump into the horse as it is completely flexible.
No, it will not distribute the weight over the horse like a treed saddle will, but in my experience, with horses developing and changing so quickly, the benefit of the flexible saddle is a priority. I believe the biomechanics of the horse and the way we sit will have a bigger impact on the health of the back and I do not prefer a saddle that allows a rider to sit through bad riding or movement.
I personally use the Ansur Classic. It is pretty much like a glorified bareback pad. It is that close. I have used it for years on a wide range of horses and have never had one complain or have any kind of back issue because of it. It is a little strange to see for the first time, and many people shy away from the lack of a gullet, but you have to keep in mind it is totally flexible so molds to the horse. For horses with very high withers or poor back muscling, I use a pad that fills in for that.
The down side is that without a twist in this saddle, if your horse is particularly wide, your legs will not hang down the same as in a dressage saddle with a twist. I have not personally found this to be a big problem, but it can take some getting used to. The Ansur Carlton model does have a modified twist by adding additional padding and it has a center gullet option. This saddle often is the best of both worlds as it doesn't feel as wide to sit in on wide horses, yet still gives the same close feeling as the Classic.
The next model is the Ansur Excel which will feel very much like a 'regular' dressage saddle. It is not as flexible and close as the Classic and Carlton, but is still treeless, so has the benefits of more flexibility than treed saddles
If I meet a horse that prefers a saddle with a tree, or I have a student with a treed saddle that fits and everyone is happy, I don't necessarily change it. The horse always is the one who makes the final decision.