Cassette tape is the ultimate Audio book format to remember location even between players (desktop, pocket, car)
The forgetting location is a big issue with CDs and cassette quality is good enough for speech. Few have speed adjustment.
Also you can store more per cassette than CD. An unabridged 80,000 word novel is a lot of cassettes or CDs, so I'm happy to use Android and Musicolet. I've always bought a phone with a micro SD card slot.
Musicolet: You can adjust speed, pitch and set a minimum duration to remember position.