I've just discovered this and it's really been a massive help. For ages now on one of my PCs, Live TV playback stutters badly. Suspecting a renderer or DXVA related problem I started snooping the registry for some insight and I found this reg key and set it to 0 to force the legacy renderer. Since then, all my stutter problems have gone and with little to no impact to overall PQ.
I relalise the majority of users will want to leave VMR enabled for TV but wondered if it would be worth including this as an option in the MC GUI just like it is for DVD and other video formats. It's certainly made all the difference for me!
Thanks.