Thanks, Bartvander and HCHeyerhahl.
Tried the 64bit Beta on Win7, 24gb. It seems to be especially well suited to sharpening already upsized images without exaggerating upsizing artifacts, which is a problem with other sharpeners I use. Runs very fast on big files. 3 gigabyte files in well under a minute and single 21mp images in the time it takes to click the OK button.
The postage-stamp preview window seems small, but it updates instantaneously and I think this is the sort of program one uses parametrically more than from visual feedback. And it handles normal, single frame files so fast it's no trouble at all to try out iterations on the full image.
For $45, it's a definite go. Only time will tell the full story, but it looks pretty darned good.