Compression ratios of fifty percent are common, which would allow listening to an hour tape in only a half-hour. I tried that. I got my cassette player and an AC adapter. I plugged it in and settled back in my rocker to listen. An hour later I bumped awake and realized I'd slept through the whole side.
Cassettes work best in the car.
Handling cassettes while driving is a potential problem. With abridged books of two to four cassettes this is pretty easy to do. But unabridged books, with as many as twenty cassettes, can be a pain to handle on the road. One of the problems is the type of binder used to distribute the sets. More than once a quick stop has spilled cassettes into a heap on the passenger floorboard.