I run regular 5/8" shaft Sawyers on my big boat and Sawyer Mini-Cobras (1/2" shank) on my playcat. Love 'em.
You'll really notice two differences vs. standard-type locks: the curve allows a smooth vertical travel, and if you run rope wraps and rubber donuts, the donuts will stay in place rather than bumping up the oarshaft (a particular problem on 1-3/4" shafts). On a flat-faced lock there's a bump when you raise or lower the oars. On a Grand Canyon trip with donuts and NRS locks, I had to bonk the donuts back in place several times each day.
We posted a bunch of stuff on fitting oarlocks— basically you need to bend the tops of the horns in so that the oar won't pop under normal stress, but under extreme stress the horns will flex enough to let it go. The Sawyer locks include crude directions on how to do this. I use a vise, a hammer, and shims rather than rocks.
Here's a site with both Sawyer flavours, and some talking points:
Duckworks Boatbuilders Supply
For most circumstances the springs allow a bit of play for hitting a blade on the bottom, etc. For extreme whitewater, you can thread or drill and pin the oarlock shafts so there's no
travel, which makes your oars more likely to shoot up through the locks or pop.