@mydavesat The instability feels like a really big hurdle initially, but you get used to it very fast (couple of weeks), and the additional instability of longer straps is trivial compared to the initial hurdle.
Think support hold like doing an L-sit on two of those
exercise disks. Initially that is really hard, but increasing or decreasing the radius of the disk doesn't really make it any harder after it is palm-sized.
Anything longer than 1.5*upperTorso is sufficient for training all but the most specific of exercises.
If you are training HS transitions, however, you are going to want to dial in
exactly how hard to swing to do it - but even for something like an iron cross, as long you aren't using the lateral movement to stabilize, its fine - the difference between a 10 degree IC and a 15 degree IC because of strap length is negligible compared to the overall force; the difference between a 3 and 5 degree lateral movement HS is trivial.
It just doesn't make a difference.