Kenko also made a set of "AF" extension tubes. They're actually "A" tubes with all the contacts, but they have extra contacts for power zoom or something--there's no AF coupling and inside the box there was a slip of paper that said "use camera in manual focus mode."
But the camera thinks there's AF, so if you forget to switch into manual mode, the screw drive spins (and echoes in the hollow depths of the tubes).
They also wouldn't allow you to use Live View on the K20 with SDM lenses for some random reason. I ended up returning them and began the long slow hunt for "A" tubes (not to be confused with "auto" tubes, because if it flicks the aperture lever for you in M mode, it can still be considered "auto").
I had eBay email me any time the Uniplus came up. There was one auction in 6 months, and they wanted almost $200 US for a single 25mm tube. I even thought about it. The Kenko Uniplus is the only one that supports AF and SDM as well.
So deadwolfbones--you got a deal (not that you didn't know that!)