You really can’t compare a 56mm scope to a larger scope. The STC/ATC is an awesome scope for what it is, I have one and my Meostar S2 blows it out of the water all the way around, better resolution, better edge to edge, brighter, more magnification and easier to rotate with the angle scope without a an aftermarket solution. The only place the ATC wins is size and weight.
I’ll still be taking the ATC on a week long backpacking trip in a couple weeks. After that I will know for sure if it’s worth keeping or trading for some NL12’s. I’ve packed around full size spotters for years and they cannot be beat.
As far as clarity and resolution the ATC is pretty much on par with my Meostar 15’s although the 15’s are much better to sit behind for an extended period.
In the end I have a feeling I might end up with a pair of NL12’s and the S2. Currently I have 10’s, 15’s, ATC and S2 spotter and it’s always a struggle to decide what to take on each hunt. I still don’t know what binos I’ll be taking on my backpacking deer hunt. 10’s are nice for a quick look but the 15’s are awesome for breaking apart country finding bedded bucks. Right now I’m thinking I’ll do 10’s on a tripod and the ATC for picking country apart and getting a close up look.