My ancient T68 have modified Eink-versions of Coolreader and Oreader builtin. It can show whole-page pdf-scans of regular books without scrolling. T68 has many shades of grey so most android apps work very well. Eink suitable for static games, like GOroid and Sudoku. Best housekeeping program is the "Total Commander", with access to Gdrive, Dropbox and FTP.
By the way, OnyxBooxx runs a rather ancient Android version - 4.0.4.