I used to use them, thought they were really great and had less knee soreness. Then I couldn't get them any more so I went back to round chainrings and didn't notice any difference. Interesting to hear they are back but I don't think I'll try them again. I don't know if it makes a difference but over time I've migrated to wider ranges of gears so now I have a 16" low and a 118" high and I think maybe being able to spin up the hills makes the Biopace unnecessary. Funny thing about the wide gearing - once you get used to it you really don't want to go back.