The parallel port driver inside Mach3 works and works well for all general work.
Where it falls over is in threading on lathes, it works for some but not others.
The new drive for Mach 4 called Darwin has just been started by Art who still owns the rights to the driver, not Brian.

I'm working with Art on a test version just for threading. Decisions will be made about backwards comparability later, by whom I don't know, presumably Brian.

The problem with the add ons like K Flop and Smooth Stepper is increased cost and complexity.
I have looked at USB devices and do not like them as you are tied to the one developer who has written in stone how it works and looks, at least with Mach you can customise to your requirements.