Katie, I’m not sure about per plant production. But I planted 3 lbs of Russian Bananas and final yield was a little over 60lbs. Rose Finn Apple, by contrast, was a very light producer of much smaller (and knobbier!) potatoes, though I didn’t weigh them. I got those from a source other than the MPL, but they were good seed potatoes. I got sidetracked and still haven’t dug the French Fingerlings—probably tomorrow—, but, based on some exploratory digging, it looks like they did okay.
I agree with you and @ltilton: they are very good simply roasted or sauteed.