The single ring can compact much better than a full UTA. A nesting UTA required a bigger mirror box.
Full ring baffles can be made. Focuser and ring rigidity are the questions.
I've read claims that single rings have shown flex, but which manufacturers? I also recall Jon's dobstuff structure flexes more than he liked. He blamed the poles, bit I doubt those 2" poles flex 1/100 enough to notice. I think the rings and their joints are flexing.
The biggest design challenge I see is how to mount the focuser rigidly.
Correct, but flexure there can be reduced by curving the plate the focuser is attached to.
And flexure of the ring itself can be reduced by making it a lot thicker, with a sandwich structure to reduce flex.
After all, a 1.5" thick single ring doesn't reduce the compactness of the design when it is stowed away in the car.
Still, focuser base flexure is a significant problem with all single ring designs with 3+ lbs in the focuser.
--contrast will suffer without great modification of the design when set up
--protection for the secondary is minimal, against dew, or damage
--a single ring necessitates longer poles, meaning more flexure and sag unless larger and heavier poles are used.
--the ultralight upper will lower the altitude axis, providing less baffling and protection for the primary mirror
--the shorter mirror box will make boundary layer fans harder to engineer and install.
--installing finder scopes is a lot harder.
So I have to ask why a single ring? What problems are solved with a single ring design that would not be solved by a short 2-ring design like the ES dobs?
It seems to me that a single ring design just causes a lot more problems than it solves.