The Sieg KX series machines use the leafboy card and have done for quite a while.
We have never had to change a card under warrenty.
Spindle is controlled from Mach3 by step and direction and the follow in is pretty good. No one expects to have the screen display the revs to plus or minus 1.
These have a brushless motor and spindle board and so are slightly different from a VFD but we have fitted quite a few second high speed spindles to these machines using a range of VFD's including the Chinese ones.

Again no problems in setting up if you follow the documentation.



This one is in front of the spindle because it's designed for 2nd opp work on a 4th axis and putting it at the side will mean both spindles are on the same centre line and get in the way.