I have the 5-20x56 on my F T/R rifle and tracking is spot on and repeatable. Its been up to 600yd zero, down to 100yd zero and back to 600 several times without any shift in POI. Glass is same as NXS (so I read many times over and having looked behind other competitors with the NXS series, I would agree) which means, good.
The Zero Stop is not as firm as a true stop on the NXS series but it's serviceable. It's possible to go about .5MOA (2 clicks) past if you really crank on it, but if you are paying attention it works fine. Mine is the IL model though I've never used it other than playing with it, which means it was left on and now the battery is dead.
I'd certainly buy another without hesitation if I wanted to stay in that magnification range.