I've ordered two packs of these - one for Dad's AR build and now one for mine!  I absolutely love them.  They provide great, positive traction on the keymod rail.
We built our ARs for hunting pigs and coyotes (300 BLK) and these provide good grip even when wet with early morning dew or from slogging through the rain and mud for hours to get to the pigs.  
A tip for installing them:  Use the side of a soft round rubber mallet to "roll" them into place until they click.  Dad and I really struggled trying to push them in by hand, but a friend said he used a wooden rolling pin.  We thought the rolling pin might damage them, but the side of the rubber mallet did the trick!  Don't hit them with the mallet, just use it to roll them down.