These are soft & flexible, as advertised, and I don't, therefore, see them breaking in the near future like the cheaper, more rigid plastic covers tend to do.
Metal Spirit Bubble Level for 20mm Picatinny Weaver Rail Rifle Sight Scope Mount
Apr 13, 2017
No mounting lug, just clamps on to rail...
It will work fine, but the design could be improved. If you want precision, look elsewhere. Most rail-mounts have a lug which runs through the recess in the rail, positively locating the accessory. This does not. Use some Loctite on the threads and try not to over-tighten the screw. I do like how it is out of the way, not protruding, so the potential to get snagged or hit is low. I have it tucked right behind my scope mount. I would probably not buy another one, but this one will do what I need.