You probably didn’t notice, but I had exactly this setup when I took lessons from you.on Feronia. Being able to twist the leathers to get a 90 degree stirrup angle was great for trail riding.
I tried some on my jump saddle when a friend at the barn lent me a pair. My usual setup is regular leathers and MDC classic stirrups turned to 45 degrees.
With the stability leathers, I had to put the stirrups back to the zero-angle position (like non-MDC stirrups), otherwise my lower leg was cranked out. It was really interesting to see the difference!
I used to get stirrup burns on my calves from the regular leathers if I wore breeches or half chaps that were at all loose - I have chicken legs so this happens a fair amount. The MDCs did help that quite a lot, but the stability leathers made a bigger difference.
I ended up buying a pair of stability leathers from Greenhawk (one of their house brands, so nothing fancy) and now use those with the stirrups hanging straight down.
ETA - I never had the calf rubbing issue with my dressage saddle so I still have my regular Prestige calfskin leathers on that one (with traditional heavy fillis irons).