I looked at several alternatives before settling on GrapheneOS. Many made claims that sounded good but only GrapheneOS had deep technical documentation. I'm not an Android developer so some of it goes over my head but I've written detailed software documentation. I know you don't write what is in their FAQ or revision history if you don't know what you are doing.
I've been using GrapheneOS for about a year and it has worked well. Only have two minor issues:
1) I'd like the ability to have timestamp data added to the EXIF image info. There is an option to have the GPS data added, so timestamp really ought to be an option too, though I certainly understand why some users would choose neither. I'll probably end up writing a Perl driver for exiftool to add the timestamp based on the image filename which is YYYYMMDD_HH_MMSS_MSEC.
2) There aren't many fonts and Roboto supplies 1037 glyphs. The card suit symbols are missing which matters to a bridge player. E-books that display correctly almost everywhere don't on GrapheneOS unless the e-book explicitly includes a font with glyphs for the suits.
I've used Calibre for years and I like it a lot. It quite good for creating or editing e-books (oh the ghastly things you see if you look inside an e-book...)
The Calibre UX is fine. The real UX divide isn't desktops / laptops vs. smartphones / tablets, but rather content creators vs. content consumers. Modern UX is oriented to content consumers but even there manages to waste too much space and has become too flat and minimal. But once your application is at least partly for content creators, a dense interface is ideal and comforting.
I've haven't experienced any data loss with Calibre except when the e-book editor crashes while checking a book for errors. This has always been due to memory exhaustion (2 GB limit) when checking books that were unnecessarily complex (see “ghastly things” above).
SumatraPDF opens EPUBs almost instantaneously, but at the cost of not rendering every aspect correctly. As I recall the documentation is clear about this limitation.
I like the PocketBook app a lot and use it to read books on smartphones. But it has some basic rendering quirks; for example it can ignore margin-top and margin-bottom on paragraphs, seemingly because it does not apply CSS precedence rules correctly. It took me five e-mail exchanges, including sending a very simple hand-rolled EPUB illustrating the problem, to convince the developers that there is a problem.
I've been using GrapheneOS for about a year and it has worked well. Only have two minor issues:
1) I'd like the ability to have timestamp data added to the EXIF image info. There is an option to have the GPS data added, so timestamp really ought to be an option too, though I certainly understand why some users would choose neither. I'll probably end up writing a Perl driver for exiftool to add the timestamp based on the image filename which is YYYYMMDD_HH_MMSS_MSEC.
2) There aren't many fonts and Roboto supplies 1037 glyphs. The card suit symbols are missing which matters to a bridge player. E-books that display correctly almost everywhere don't on GrapheneOS unless the e-book explicitly includes a font with glyphs for the suits.