Most of the posts are shooting past the target, ime ..

It is very very complex to have an actual usable cnc controller ..
and they all have lots of shortcomings independent of cost.
The errors vary with mill and lathe.

Endless issues with front back toolposts, metric-inch, offsets here and there, macros ..
Lathe threading properly is very very difficult.
After about 2000 hours of work and use and 8000 in kit .. and 4 different solutions discarded as not working ...
(stepperworld-kit drivers-gecko 201s, 203s, 320s, and pp, warp9 ss, centipede, cslabs (using))

The chinese cheap controllers seem to work quite well for mill stuff and for routers.