.. I've just tried using clipless pedals (spd 515's ), easier to learn than I thought. They certainly feel better for riding hard. only used them for 2 rides so far, and generally they still can feel a bit strange too.
Prior to using them, I've had a case of some strange knee sensation for a couple of days after a hard ride (-> alarm bells -> took up policy of only a couple of harder rides a week & low gears+high rpm ).
... so I'd like to know if they're going to have more or less risk of joint-strain.
I'm cycling mainly on a commute-as-daily-excercise-and-recreation run ( 18 mile round trip, 3 weeks now, rest day midweek ), so I guess long term sustainability is more of a priority than outright efficiency .. at the same time improving my times is fun.