As somebody who listens to audiobooks while commuting and biking:

1. You can't everywhere. Two effects that are critical: -with good earplugs you don't hear the environment anymore -an interesting audiobook can pull you in. you space out

when you drive a car your reaction suffers hard. when you work out, especially during cardio, you might focus less on the stress of the exercise, a positive effect. when you are in a bus or train, you might miss your station. and the flipside: if something demands much attention, you can't focus on the audiobook and miss a part. I usually don't rewind, unless I don't understand what's happening.

1. there are abridged and unabridged audiobooks. the latter has all the information that the book has, so I wouldn't bother reading something, if I already have taken in the information via audiobook. but I do listen to good books multiple times.

also: audiobooks, at least for me, are only an alternative to the classical book if the subject is not too hard. therefore textbooks on academic subjects usually aren't suitable. same goes for hard to understand texts like works of nietzsche etc

1. maybe. depends on why you are having a hard time.

if you lack focus then audiobooks are harder to consume, because backtracking is very tedious. if all you lack is time or you don't want to carry a tome around with you then audiobooks are godsend