Yes the IP-M does support slaved axis and does it very well but it doesn't home to individual home switches. This means you can't square the gantry using a switch for each screw.
This is important because when steppers turn on they often move to the nearest full step and if one motor jumps opposite way to other then over time it racks the gantry. So homing to separate switches allows you to square gantry back up.

I use lots of the IP-M and have been pleading with Cslabs to provide homing to separate switches but they are not too keen. I think because they don't want to hurt sales of the IP-S which I feel is wrong way to look at it. So I encourage you and others to email them and complain. Let them know that you would be prepared to buy if it had this feature and would never buy the IP-S for stepper system because of the higher price. Maybe if enough do this they'll re-think.? They did on making it Slave so they may again if enough people ask .!