The biggest problem I see with a round column machine other than the low mass and limited table travel is the limited Z-travel in the spindle and column. The table travel can be overcome by repositioning the head on a fixture, a PITA but doable. But the spindle travel becomes a real issue because you usually have at least a couple inches of travel over the arbor for a lot that guided tooling. That eats up your spindle Z very quickly and when you go to raise/lower the head on the column, you lose your x-y center. Unless they have been modified with a guide rib on the column, most round columns lose control of x-y when moved in z. So keep that in mind for any machine you want to do head work with. Z-axis is usually where the limitation manifests itself. Even on a Bridgeport type machine it can be an issue with some of the tooling. You ever use one of those coax indicators to center over a hole and then go to an endmill in the spindle collet? The two tools are about six inches different in length and the the spindle gets used up and you have to raise/lower the bed every time you switch tools. At minimum it's a compromise and for a lot of machines you can't get there from here.
I'm pretty familiar with the issue when using my Index Model 40 mill to repair BMW oil pans, a little side hustle I've had for a while. Requires several drilling, boring, threading, milling operations and when you switch from the boring head to a chamfer tool in a chuck, to a tap, you are looking at 4-5" difference in tool length and I only get about 3" spindle travel so I'm winding the table up and down quite a bit. I'm in process of making dedicated tooling so I can get away from the boring head and drill chuck, but it's well down the list of to-do's.
