Yes. I used one for a night in a forest in Snowdonia (I think it was April, some time in spring anyway). It snowed on me. It was cold and uncomfortable, but I survived. I wouldn’t choose to do it again though,
I’ve also slept in one on a summer night in deepest Surrey, but with a sleeping mat. It was not all that cold, not so uncomfortable, and okay.
They are noisy and cold compared to a sleeping bag, but very very light / small. It is a bit of a hassle to repack into the stuff sack, but doable.
Personally, having experimented with it, I wouldn’t plan to bivvy in one of these, but it is a handy emergency thing to take out on a very long ride just in case.
Joe