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I use them for pictures in frames up to a couple of kgs.
A mirror like the one in the picture I would put a rawlplug in the wall or use the metal plasterboard fixings if it's plasterboard. Then probably mirror hooks as they make sure the mirror is always level.
If the mirror in the photo was above a sofa I would consider that a serious risk to any smaller residents.
I've never used a thunder bolt but they don't look like they would be my first choice unless I was fixing steels to concrete.
I’ve used them a lot with no issues except for the one mentioned and it was a cheaper type of hook. I will report any further issues. Oddly the last heavy mirror I put up, I used thunder bolts - and would recommend them for heavier stuff.