i my opinon rental agreements are null and void, because devorim shebelev ainun devorim. BUT i am not a posek.
If it wasn’t printed on the CD jacket, you’d be right, but it is.
Better question – if it is so effective, why aren’t ALL the producers using this rental setup? Why only Aderet?
You would have to ask them, but my guess is because some people are upset about the rental, as evidenced here. It’s probably a business decision.
BTW, Aderet is a distributor and not always the producer of the CDs they distribute.