Love mine.
I have the old school Herm Sprenger’s and the MDC Ultimates.
I have two knee replacements and an ankle patched together with screws, wire and bone grafts.
The Herm Sprengers are good for easing fatigue and general joint pain.
The reason I got the MDC Ultimates in particular/in addition is that I have difficulty turning my toe in on my injured right ankle, which makes it hard for me to catch my offside stirrup. I was either fumbling, or using my stick to help hold the stirrup out so I could catch it. I realized this was really a safety issue, both at mounting and it I ever lost the stirrup while riding. If I remember to position the MDCs (90 degrees for me) before I mount, the stirrup is right there when I swing a leg over.
I will forget and not think it matters, and then I’ll ride in tack with a plain Fillis stirrup and be in agony after 45 minutes.