Mach3 has a lot to offer but it has its down sides as well. Mach4 looked to be like it was going to be great, it probably will be and maybe even is, as I haven't tried it for years. The downside for me was that I would have to learn Lua and I wasn't willing to do that as I had enough trouble with learning VB.
I will at some point try out SimCNC on the Chiron but again that will mean learning a new language so it may not progress very far.
The SZGH on the lathe seems to be working well for me so far and I have been able to do all I want with ease and the programming language seems to be a kind of home brew but is very simple which suits me
One thing I really like with the SZGH is I can press Hold and it is instant, I can change screens, look at parameters or whatever while it is running and there are no issues.
As said it is not as adaptable as Mach3 but no way I would go back now on the Lathe, mill is a different thing and I am quite happy with the CSMIO and Mach on the Chiron but the instant feedhold and overrides would be nice