The only to soft-tails I've ridden are the Moots YBB and the Salsa Dos Niner.
I rode the Orange and Silver versions of the Salsa Dos Niner as is seemed Salsa was always adding more material to the rear of the frame for each new version in attempt to stop the frame failures that happened at that end of the frame. Both of my frames cracked at the shock mounting bolt. They were amazing riding frames, but they lacked lateral stiffness. This was only noticeable for me when i was going fast down a mountain and carved into a turn. It almost seemed that the front wheel and rear wheel were tracking on two different paths, until the rear end seemed to almost hop into the same track as the front. I suppose that flex is what caused my frame failures.
This frame reminds me more of my Moots YBB. Even though my Moots was a 26" bike and only had just over an inch of rear travel, this frame feels as solid as my Moots. The big differences are that this frame is for 29' wheels and is getting just over two inches, 50mm, of travel (by my rough estimates), so it is a much more plush ride.
The seat-stay cut-outs, besides looking cool, seem to add small bump compliance from what I was able to ascertain on the web.
My main focus in getting this frame was two-fold.
One, maintenance free suspension. My full suspension frame has become a yearly ritual of replacing all the bearings (two times already). For this frame, it will just be shock maintenance.
Second, as I am well into my 50's, I started riding dirt when hardtails were the bikes to ride. I still love the feel of a hardtail, and how it connects you to the ground, but as I age, hardtails seem to tax my body more and I need more recovery time in between rides. After thirty years of riding, I finally picked up a full suspension to be able to increase my ride frequency due to shorter recovery times, but even my short travel full suspension, feels like I am missing that direct connect with the ground.
This frame is the best of both worlds. I am glad I saw QuentinLL's thread and decided to pursue this build. The two inches of rear travel is enough to shorten recovery times between rides, I can do 25 - 35 miles of riding over consecutive days, but I sill feel a solid connect to the ground when riding. More riding is important to me as I age.
More pictures to come.