I can't say much about the USO level as I've never been around one. I can tell you what a handful of us use & have had really good luck with. I strongly recommend the FlatLine Ops level. You can get one right here from Len in the LRH Store:
Scope Level By Flatline Ops
These things are bad to the bone & very well built. I also have a Holland which is a good unit. The FlatLine has two advantages over the Holland:
1. If folds out of the way when not in use however, can still be used in the folded position.
2. The FlatLine is FAR easier to set as it employs set screws under the magnets to fine tune the bubble level (genius).
Hope that helps.