> How do the current listeners (on HN) of works here decide what to download or not? Or is it just a matter of “download, listen and see if it’s good enough or move on”?

Pretty much download, listen, move on. But after a few, you might start recognising the reader, and have confidence in them. (It's been a while for me since I made heavy use of Librivox, so I've forgotten the ones I preferred.)