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I have these in white.
Fairly good. -
They are decent, not perfect fit but not bad at all. Never had any issues with them pulling away, the faceplates need to be levered off with a screwdriver or similar:
They are these ones so fairly budget end. https://www.ukelectricalsupplies.com/selectric-5m-plus-screwless-satin-chrome-2-gang-13a-dp-switched-socket-with-grey-insert.htm I already had them installed when I moved in but had a few extra fitted and the electrician didn't make any comments (positive or negative).
Most are level but I do have a few that are a bit off (the whole house has them). Hadn't considered it being an issue with screwless ones.
I don't know generally but my screwless ones just use a standard back box. The main part of the socket attaches as normal and then a thin faceplate just clips over it.
Edit: I have these which might actually meet your criteria