srock wrote:
Aside from the efficiency it would also be less fatiguing as my feet want to slip down at the heel.
Aside from the efficiency these slings work pretty well.

But considering efficiency, these also work quite well. While you may not be able to pull back with the intensity of a clipless, you can see by the angle of the strap that you can pull the pedal back with the heel without the strap disconnecting. In fact, you can operate the Drive to a limited degree by pulling only (no pushing).

Here's a link if you want to make your own. Search the forum for some other designs as well.
viewtopic.php?f=11&t=31555 But if you want the clipless, you need to get the old style crank arms.
