As a follow-up to this post, I ended up buying a set of Pro-Loks and using them on a September trip down the Middle Fork of the Salmon. Absolutely loved 'em. I had used convertible oar rights with Cobra oar locks for a long time and won't be going back. I ended up rowing a boat with Cobras/oar rights for half a day on the trip and the difference in friction was remarkable.
My only complaint is the wear on the oar shaft (I use Cataracts SGG oars), which I think I can solve with a bit of Gluvit. That will be a winter project for me.
Since I split my rowing time between fishing and whitewater, I bought a set with heavier water in mind (recessed hose clamp to reduce possible lacerations, nylon cord versus wire to reduce accidental garroting, greater tension on the set screws). I think he still makes the one pictured above for milder water.