I was first introduced to them on the Kubicki Factor and Ex-Factor years ago. I ignored them until recently when I purchased two basses that I could not use Dunlop Straplocks with. I wanted better buttons (those Schaller style strap lock buttons don't hold any strap in without Schaller locks and I don't use them nor ever will) so I ordered the Gripper's from Stewart McDonald. Voila! Amazing how well they lock a strap in place and also amazing how easy it is to get a strap, even one with stiff leather, over them.
So, thanks Phil K. for reminding me what is good.
Gripper Strap Buttons just rule...
Gripper strap buttons rule! 
