I've used the top of the adjuster cap in the past, but I'm not likely to use one on a LR rifle, just on short range stuff.
It is too bad that Wheeler didn't opt to make those levels with aluminum instead of plastic. I'd have a lot more faith in their rigidity and repeatability if they had.
Wheeler does make an aluminum version. I leveled my gun using the wheeler kit, then set the scope with a plumb line.