Also about the idea of taking parts of... I'm not sure what happened my partially finished note got posted. Anyway, I don't think stripping an eZip and adding stuff to a Mongoose would gain much. You'd have to move the rear wheel, with motor mount (and find a way to attach the mount to the mongoose). And you'd have to move the rack and the battery or batteries. The batteries packs are what makes the eZip heavy. They weigh 16 lbs a piece. I carry one pack on each side so that adds 32 lbs to the not too terrible 58 lbs the eZip, by itself, weighs. It's that 90 number that makes me say HEAVY. If I were Cathy, 127 lbs even that 16 lbs single pack is a pretty significant % increase.
I weigh about 225 but am in pretty good shape, I regularly get 25 miles from the two batt packs on HILLY roads with considerable exercise. That 225 is 10 lbs less than when I got the bike. It does allow more exercise because you can use it for transport.