PLLphotography wrote in post #16341159
do you find that thumb grip helps with stabilizing your hand-holding with a manual lens?
I have 135mm f/2.8 manual lens and I get nausious sometimes trying to steady myself while looking at the viewfinder lol. Now, I have a 70-210 f/4 Canon FD lens coming my way, and it'll only get worse

Have to admit that I haven't used it so much that I could say it's useless, or not. But the thumb grip, being this short, is located above the screen. And your thumb would go over the screen covering part of the screen, and even possibly touching the screen.
But I have to be more on the road before I can say anything more.
70D. EF 70-300mm L, Tamron 90mm F2.8 VC and Sigma 17-50mm F2.8 OS HSM.