You can check their capacities and speeds with software like cpu-z.

I’m looking for the same. I’ve used moon reader on android and it can sync progress between devices. Also it supports WebDAV, so calibre may work but I haven’t tried it

I mean that the abstraction and “security” measures have made it very difficult to get where are the files. It’s not thinking in any app in particular.

To give you an example:

• descent( boardgame app), we tried to get a backup of the campaign in progress to change the phone. But there was no easy option on the app and the phone wouldn’t let me access the directory where it should be saved. (Funny thing is that it was only blocked on the phone we wanted to backup, on other phones we were able to access those files)

Don’t forget the old stuff folder inside another old stuff.

Seriously tough nowadays it seems harder to organize, everything is in the cloud or in an app.