The backlash thing and some CV issues and threading problems are things I am watching to see if they get sorted out before I take 'the plunge' and commit to Mach 3. I already have a fairly big investment in time into Mach 3 and so I would want to use the same control software for both mill and lathe.
The backlash, as noted in the documentation, is really only good for things like increasing the precision of drilled holes or things like that. The implementation currently in mach is not useful in my opinion for general machining because of the pauses when the slack is taken up. I simply cannot use it for milling.
I watched a youtube video from Hossmachine where he has to use backlash compensation just to get a round hole. I'm not nearly that bad off, but I did have .005 on both x and y and a good deal more on Z.
My solution has been to buy oversized balls for the leadscrews. I located .0009" oversize balls on ebay and they have taken the lash to less than .0005" on the X a little under .002" on Y (my problem axis) and I designed and built an entirely new mechanism for the Z and it now has only .005 and I am waiting on the new oversize ballscrew bearings for that axis to get that number down . . I am hoping for .002" or better.
For my purposes, this will be accurate enough so long as it can hold or a while.
I am no expert in CNC control programming by any means, but it does seem to me that adding the backlash amount to the distance of first movement after a change of direction (per axis) would not be a difficult thing to accomplish. While that would not be as accurate as stopping and taking out the lash and then proceeding (with jerky, tool burning pauses), it certainly would increase the accuracy of the machine while maintaingin a smooth CV. That would not be a perfect solutio, but in my opinion it would a logical and valuable compromise between the current 'useful for drilling, useless for milling' gap.
You mentioned that there is a change in the backlash comp behavior in your software that is version dependent. Can you elaborate on that please?