Audiobooks are pretty neat, but unfortunately studies show (feel free to imagine a soyjack here) they're pretty garbage for retaining information. I've noticed the same just empirically, information read from a PRINT book on PAPER tends to stick around in the brain much longer.
If you want free audiobooks Myanonamouse is unbeatable. If it's on Audible or other services it's on there, and if not requests usually get filled within a few hours.