@aard most importantly, it notifies me when the printer needs my attention (e.g. change filament). My biggest annoyance (and what I wanted to fix/change) is that their app icon is not a proper vector graphic image, so it doesn’t look good in themed Android launchers.
@bluewing I am sharing my personal experience with the MK4S, since I went down from a 256^3 printer.
Belt tensioning on the MK4S Kit was a pain to do, so I am curious how belt tensioning for a core kit will go. I hope they give a better solution than the tuning app, as tensioning belts for a core xy is noticeably harder.
Neither of these are blockers anyway, like I said, I am happy with my MK4S.