There are about a half dozen around my neighborhood. My daughter and I constantly move books in and out of them to keep them fresh on our walks.
Sometimes they’re great; but, oftentimes I find them to be utterly and completely devoid of anything interesting or different. Almost every single one has some sort of religious spam in it.
I find that they're almost always a perfect cross-section of the local thrift store's books - including the absolutely inordinate number of cookbooks.