Yev from Backblaze here -> Yea, we've tested them but found they didn't play nice so we aren't deploying them in droves. If you find a good place for data on SMRs send it our way, would be fun to read up on it!
Did you try host-managed SMR? Seems more promising, although significantly more effort.
Not sure on that one actually. I think one of the main things for us was the rewrite performance, since we're constantly moving/copying/deleting/changing data we need that to be fairly performant - but not sure about the host-managed drives!