The readings are surprisingly well done. The readers do as well as the "professionals" doing most of the commercial recordings I listen to. Audio level has been dead flat on most of them, instead of ranging from "mumble" to "yanking earbuds out" like a few commercial outfits who should really watch their quality control better than they do...
Anyway, two that I just listened to were The Colors of Space and The Door Through Space by Marion Zimmer Bradley. I'd never read The Colors of Space before.The book was originally printed in 1963, and would have been a "juvenile" at the time. Nowadays it would be a "young adult." The storyline is probably more suited to early teens than later, as some of the happenings were a bit simplistic (at least by modern standards), but it was still an adequately entertaining story.
I'd owned a copy of The Door Through Space in high school, and read it two or three times before trading it off maybe ten years later. I was more into hard SF then, and it simply ran afoul of lack of space to keep it.
I remembered bits of the story, but it has been... at least 30 years since I'd read it. Listening to it this time, I caught a lot of things I'd missed before, or simply forgotten. For 1961, it was pretty racy - topless women with nipple rings, light bondage, and heavy S&M. I remembered the wrist chains, but had forgotten the rest. I guess as a hormone-driven teen, I was pretty innocent...
One thing I had remembered was that the story seemed to lose momentum near the end. Viewed from the perspective of decades more maturity and experience than last time I read it... yep, it fell flat on its face. Bradley wrapped everything up, but a lot of it had the feeling of being quickly done, and the writing style changed quite a bit from the beginning to the end. Maybe it was something she had laying around that she finished up for sale, or maybe the end was even racier than the beginning and got cut by offended editors, or something.
If you've read any of her Darkover books, The Door Through Space seems eerily familiar. Wikipedia says the first Darkover story was printed in 1958, so this might have originally been a Darkover story that didn't fit well into that series and got edited into a standalone novel.
If you liked good old-time fantasy-adventure of the Leigh Brackett style, you'll probably find The Door Through Space entertaining. If you're mostly familiar with Bradley's later Darkover books, you might be put off by the difference in style. But it's still worth listening to, and, hey, it's free:
https://librivox.org/the-door-through-space-by-marion-zimmer-bradley/