Thanks for the feedback, folks. I didn't realize the non-Presto Helios was a 20-incher, so that's good information. Other points: Yes, I do think weight matters when carrying a bike downstairs, then loading it through a small opening in a car (harder to control passing the bike through when you're trying to keep from dropping it). No, I don't think chain grease is a major issue. I don't over-grease mine, plus - as Thor said - I wouldn't rest the bike on the drive side.

So I need the gears of a Brompton, and the weight of a Presto Lite. Great!