I can't imagine putting my mare in that for vet exam... She would probably go crazy and injure herself on this stocks. When the vet was doing to her what the vet in first picture is doing (I think it's called palpation in English?) we only put 2 hay bales behind her. She was sedated though...
I find horses are actually surprisingly calm in there. I've seen a couple nutso race horses that are a pain to get to the stocks and in there, but as soon as they are in there are fine. Even when baby gets irritating and moved in a stall and out of site.
It's pretty squishy so it must be some form of a comfort. If they were sedated it was pretty mild.
The one time I had a horse with a bad injury, I would have sold my soul for a crush(that's what we call it in Australia), even a dodgy one. It definitely makes life safer for a vet, and ergo for a horse. All it does is restrain them, because if you think that you can hold your horse still and straight if she doesn't want to, you're delusional.