One thing that surprises me, is that there are not more people using the KFlop+KStep combination
I can tell you exactly why.

1) The lack of a good, easy to connect breakout board.

2) Having to write C programs.

It's too complex for the average person to use, when there are simpler options that work just as well.

I have a friend that was fed up with Mach3's bugs, which constantly caused ruined parts for him.

He bought a KFlop, but didn't have time to install it.

I had him buy a UC100, which he could switch to by just plugging in the parallel cable, and he started using UCCNC until he had time to switch.
He also bought a second machine for his business, which already had a KFlop installed.

With the updates that UCCNC have made to their software over the last year, he now sees no reason to switch to the KFlop, and will be selling bioth of them and moving the second machine to UCCNC.