I own a Kestrel and my buddy owns a Mantis. I would not trade mine for his. The Kestrel and Mantis are both high quality but I like the leg strap design on the Kestrel better. The Mantis shape is not articulated to the shape of the butt...the Kestrel is.
I used to own an old Trophy Line but I hated it. It was heavy, uncomfortable for walking and gave me bad hip-pinch. The new generation saddles beat the crap out of those old time saddles IMO.
I really like my Kestrel, but like most saddle rigs, I've modified a few things. I doubt many saddle guys leave their equipment stock. Most of us change something. I changed my bridge rope to Amsteel and I replaced the prussic hitches with Ropeman1. Other than those mods, mine is stock and it does the job nicely. I've had many dawn to dark sits with great comfort and made 2 perfect hits on the 2 deer I drew-on this year.
There is a bit of a learning curve, but for me, it was a short curve. I shoot fine out of it, and I can hunt from a greater variety of trees than I can with a simple hang-on stand.
Foot placement tends to be one of the bigger issues for newbie saddle guys. It basically comes down to 2 choices...a ring of steps (ROS) or a mini platform of some sort. Tethrd has the Predator platform. It's ultra tiny and weighs about 3 pounds. It's easy to carry thru brush because its so small. I can't carry a traditional hang-on stand nearly as easily. The Predator is super easy to hang or remove and is rock solid on the tree. I much prefer it over a ROS but there are saddlers that love their ROS.
It seems that both Aerohunter (Kestrel) and Tethrd both are a bit challenged to fill orders quickly. They are catching up but there has been some frustrations getting orders filled without a loooong wait (months).
Anyone that's considering ordering saddles or related gear should do so soon. If you wait until next summer, you might not get your stuff in time to get practiced before the season.
And as said in post #17...even if you only hunt from a traditional hang-on style stand, you will love a saddle for hanging them. I can't even begin to exaggerate how much nicer it it to hang stands while suspended from a tether as opposed to being attached with a lineman belt.