Thanks to a tip I read here, I picked up a couple of these at 9.99 apiece. I finally got around to trying them out. I was slapping together a quick utility shelf to hold a couple of battery chargers in my garage.
If you look at the far clamp in the photo, you'll notice a small gap between the clamp and the wood (see the shadow?). I re-examined the clamps. Turns out the "pin depth" is adjustable. It was evidently set too deep for the pocket hole and wouldn't allow the clamp to sit flush.
I may try fastening another couple of scraps together sometime soon, to see if the clamps are more workable when properly set for the hold depth. Oh, and having a permanent, usable home for the battery chargers is a lovely thing indeed.