Jon
"what are the work-arounds to the round column issues on these mills?"
The first thing to consider is the work that you are likely to use the machine for. My interest is in the smaller end of things so the limitations are not so bad. The quill has a travel of 4 1/2 in. (114mm) so you need to plan your workflow to ensure that all those things that need to be done without moving the head can be achieved ( this includes tool changes). If you do need to move (rotate) the head then, of course, you will need to return it to the same position afterwards.
There are a couple of ideas for this. There was, a while ago, a design published for a location jig ( In M/E ..or maybe "the other mag" ?) . This consisted of a block with two rollers which clamped to the mill column and a hardened tongue which fixed to the head. When setting up the machine the clamp is adjusted to the correct position on the column to engage the tongue and tightened. If it is necessary to move the head it could be raised (and any tool changes etc. made ) and then lowered again with the tongue guiding the head back to the original position. Another possibility would be to fix a laser ( the sort that projects a thin line of light ) and set it to a datum scribed on the wall.
I guess your decision is :- will most of your work be within the " 4 1/2in " quill travel and how cheap is the machine you have seen? From choice I would not now go for a round column machine but nothing else was available when I bought the mill. Whilst it is a bit inconvenient it does what I need and, as others have said, it is a beefy drill!
Norman