I ride a Bike Friday pakiT, 16" wheels, and sometimes use a motor. There are tradeoffs. Folders come with smaller wheels - better acceleration but much more road feel, not always in a good way. And some potholes can swallow their tires whole. Otoh, a folder which rides as a good bike that also happens to be motorized, can be amazing if you commute using bus or rail. Easier to tote up stairs or get into elevators, easier to get on crowded trains. And then there is theft issue - a nice folding bike can often go in the office with you rather than get locked up outside where it can be vandalized or stolen. Same when going to stores and such. I'd say if you use it for transportation a folder is fantastic; if you use it purely for exercise it may not be as ideal.