Fly cutters are not normally used on the smaller mills like the X1 and the MF70. You can use some small ones on the X2 but it is still a flaky process. What is the maximum shank size you can use? and do you have a R8 spindle?
Also if I am not mistaking the MF70's lowest RPM is 5000, is that correct? if so you do not want a fly cutter spinning at that speed.