It's interesting, my complaint with Calibre was always performance rather than UI - it can be surprisingly slow for processing & converting mostly-text formats.

It's interesting, my complaint with Calibre was always performance rather than UI - it can be surprisingly slow for processing & converting mostly-text formats. But the sheer number of features & formats makes it worth the downsides. Indeed it's probably a good reminder to me as a developer, I can get too focused on making things snappy, efficient and pretty where perhaps I could have delivered twice the features if I took a little more of an 80/20 approach.