
And you can't just pick a random floppy disk image, stuff it onto a CF card, and use it in one of these PRODOS cards.

So, not everything can be used on those drives. The CF cards require software made for PRODOS (or adapted to at least load from a PRODOS drive). The emulation is so accurate, the computer cannot tell the difference to a real disk drive. Those images will even work with software using disk-based copy protection schemes. There is even a disk format which includes exact timing information. Almost all software which used to work with disk drives will now work with a floppy emulator.

And there are sites with countless floppy disk images. There is a huge software collection based on floppies. Floppy drives were pretty much the standard for the Apple IIs.
