Hans wrote,
Columnsets are rather special and mostly meant for magazine like documents, where content can span columns, images are explicitly placed on the grid, etc. For that reason columnset soperate on a rather strict grid that gets setup based in the lineheight and although content can be larger, the grid dictates what happens. Balancing is semi automatic and nearly always demands some tweaks.
In our use of columnsets, we do have content that can span columns (but we keep it outside of columnsets). We also have images within columns that are placed in the flow of text via hangarounds. We manually tweak our column lengths on each page (e.g. \setupcolumnsetlines[columnset10][1][1][42]), in order to avoid the worst of the widows and orphans. As you say, balancing requires manual tweaks too, but it's not that big a burden, since we're already doing \setupcolumnsetlines for many pages.
Using columnsets for a large document that has to flow automatically is therefore debatable. Regular multi columns or in mkiv mixed-columns are a better choice then.
We have tried to port our code to mkiv, but have so far found been unsuccessful. (But are trying again now, having found new success with TL2013 mkii.) Also, we've been unable to find any statement that mkiv is out of beta status. Moreover, much of the documentation still seems to be oriented toward mkii. So it's hard to justify much of a time investment in porting production work to mkiv yet. Can you comment on the official status of mkiv? Regarding mixed-columns: I understand it's a rewrite of the old "columns" model. My impression is that "columns" didn't support manual tweaking of column lengths (like \setupcolumnsetlines). Does mixed-columns support such a thing? That would be a critical question for us, as it wouldn't be an option for us to spend time porting to mkiv and using mixed-columns, if it doesn't allow us to tweak the height of each column on each page. Thanks again for your help and advice. Lars