I’ve one of those classic Warco round column mills, there are two issues, the Z feed is hopeless from an accuracy point of view unless you have a digital readout fitted, when it becomes absolutely fine (The readout shows exactly the nature of the inaccuracy too- ). X&Y calibration seems fine off the shelf, considering it’s a £700 machine tool. The other “fault” is that you have to think a head of a series of ops to ensure you will not have to move the mill head between cutter changes and lose the set up. The first I fixed early on, the second is no where near being enough of an issue for me to trade it in for a “square” column mill.
If I was buying new today I’d buy an X3 or equivalent rather than the round column. Always provided that the rigidity was the same or better. I would not trade rigidity for a square column.
Bear in my I’m a pure hobbyist, I don’t need to make a living off my machines or have to satisfy a customer that my work is “to spec”.
Steve