I'm sure someone will be along to help you directly. Not an expert, but the twenty isn't anything like as compact on mass transit as many of the more modern folders, though it is a very fine and excellent riding bike. I'm not sure about the weight issue though, so we'll have to wait for a more expert helper. If you're looking this afternoon at the twenty, fold it up and then picture getting onto a train with it (or bus). For real compact folders, bikes like the Brompton (expensive) are unbeatable, very closely followed by Dahon Curve (almost as neat) which comes in two forms, the D3 which is cheap, and the SL which is more expensive, but with some nicer features, especially that it weighs next to nothing.
New bikes will cost a lot more obviously than an old twenty - you'll need to assess the fold though.