OK, 1/4 season update. I've hunted from the Tree Saddle quite a bit. On my long hikes in on public, the light weight of the saddle/small platform has been a huge plus. Twice last weekend I did a nearly 1 1/2 mile hike in to hunt a secluded public spot and carrying just a tiny platform and wearing the saddle in helped a ton. Comfort has been great, also. The one time I would tell you all it was not as comfy was when I hunted a tree that had a serious lean. I needed to be on the side of the tree that was leaning pretty hard downhill. This put me at a weird angle and I had to keep the tether really short due to the angle. Other than that, on normal tree setups, I do not begin to get uncomfortable. Situating for shooting has not been an issue, either. Last Friday, when I had a good buck working to my right (the toughest spot for me to shoot), I was able to quietly and quickly turn my back to the tree, stand on the platform, and be ready to shoot.
The most substantial negative I have found, mainly last weekend with colder temps, is that my Trophyline Tree Saddle covers up my jacket and pants pockets. The new Mantis and other saddles that are lower profile might not, but mine does. It's tough to keep my hands warm if I can't access jacket pockets. To remedy this, I found an insulated hand muff online (Sportsman's Guide, under $10), and it arrived last night. I tested it and I can wear it over my saddle, so problem solved.
The other thing I picked up to experiment with is a military surplus pouch. I already have a couple of pouches mounted on the nylon loops of the saddle (they came with it) that house my lineman's rope, tether, and strap on gear hooks. I bought the extra pouch because I want to be able to cut out carrying my backpack all together. The extra pouch will hold my flashlight, knife, headlamp, and tag stuff. It's hard for me to not carry the pack but it would be a huge plus on the long hikes to not have something pressed to my back.
I have zero plans to go back to hunting a hang-on treestand right now.