Here's a rubber version for wood oars— probably attached with nails. The clip is from the <www.rainboat.com> catalog. To search it on their website, key in the part #OAR0300.
I used the hard plastic Oar-Rights my first season rowing (after many years paddling). The first thing I disliked was that when you dip a blade in the water it's fully engaged. If you dip one oar by mistake (coming off a drop) it can spin the boat.
Being able to keep your oars in the water feathered can be a good thing, besides other advantages: less windage, more natural stroke, and rotation of the grips is easier on hands & wrists (i.e.
if the grips don't rotate, your hands do— blister city).