I use an IP/M with a slaved axis. These days, I home it using a trick that someone described a year or two back. You can go into the CSMIO config plugin control panel and select "no slave axis". I then have a specific "home all" button which runs a homing macro that homes X and A together (and actually Y as well but that's not relevant). I have fitted a home switch to the A axis and it all works very nicely. Then back to the plugin, re-enable the slave axis, and off you go. I keep meaning to test whether I can use the "offset zero" field in the Mach3 homing parameters to make fine tweaks to the A position but I haven't got round to that yet. The IP/S does all that by itself, of course, but it's an awful lot more to pay if that's all you need it for.

Personally, if I were starting again today, I would look very seriously at a UC300ETH and UB1 combination which appear to be very similar in capability, 24V interfaces, etc, to the CSMIO and with the possibility of losing Mach3 which causes me just enough problems to be irritating but not quite enough to bite the bullet and upgrade. There are other options, of course, but the thought goes through my mind that I could probably do a brain transplant on my current control box without major re-engineering that way. Losing Mach3 itself for something that is not years obsolete is attractive as well...