Thanks, Todd & Rover. I, too, thought that I had read months ago that the Kobalux 28 was a dog while the 21 was superb, but I can't remember where. However, the PP SQF results appear to be very, very good. It looks big & bulky in the picture & unfortunately Adorama doesn't provide any specs re size (or anything else).
Yes, the Voigtlander 28/3.5 is $110 cheaper, but when you throw in the finder, the Adorama/Kobalux is actually a $34 savings. As a close-out, Adorama may even be coaxed to negotiate that down a little bit more. In favor of the Voigtlander is that it appears to be much more compact - a big plus in my mind.
Stephen Gandy says that the Voigtlander 28 finder is superb. I wonder about the Kobalux finder? Now if it's true that the extremes of the finder built into the R2 match a 28 mm frame & I don't need a finder at all, then it's no contest.