Smoothness? You mean the focuser?
I compared it also with an uncoated Prinz 76mm F16. I rate this scope highly.
However the Chinese refractor gave a much sharper image - it was pretty obvious.
Perhaps it was just luck - will try again another night.
No, the optical figure. You can see it in the out of focus diffraction pattern. Smooth optics will show a very smooth outer ring. Rough ones will show "hair". It gets more involved, but that's a good start.
My 80mm f/11.4 Vixen could hardly be any smoother. It's up there with my AO scopes.
-drl