I've fiddled with many different scope levels from every maker. They all have some issues, most notably, when you mount one (and it's tube attached), there is a tendency for the level to rotate as the fixing screw is tightened so, it becomes a situation where you must compensate for the rotational movement prior to tightening the locking screw. Not a big issue, but tedious.
Probably the best level is a rail mounted one because there is no tendency for rotation but rail mounted levels can have intrusion issues on short magnum bolt actions and/or actions with split mounts because there won't be enough mount area to accomodate thelevel.
You also want to look closely at the way the vial is secured in the level itself. Good levels will have an internal circlip securing the level in it's bore. Glued in or press fit vial will eventually get loose and lost.
The Vortex tube mounted level covers all the aspects of securement and is priced about 2/3rds of everyone else plus the come in 1.00", 30 and 35 mm id.
Flat Line OP's makes a nice one that takes their Angle Cosine Inditator as well, but it's pretty expensive compared to the others.