I would certainly commend your choice of the Roo El if you are looking for a folding electric bicycle, but you may suspect if you read my other posts on this forum that I am a shade biassed. In that case you should look at A to B magazine, which gave a favourable review to the 16.8 volt nimh model introduced in 2005 (now discontinued, apparently, because Dahon find it too expensive to buy in the Sram Sparc system, rather than source components directly in China).
The current issue of A to B reviews the nano Brompton, and while generally not favouring any folding electric bike, the magazine does single out the Roo El as the only one worth having to date (to which they now add the new nano Brompton, but that recommendation is valid only if you can put up with 16 inch wheels, and need a really small volume bike for intermodal journeys).
Since I first started using the Roo El over a year ago I have of course looked at other models, but have found none which are as light (not even the latest models using Lithium batteries), and none which incorporate a five speed hub gear, two motors, and the electronics all enclosed in a single casing in the rear wheel).
Other more subtle advantages (over others I have read about) are the gentle start when the pedals are first turned (no kangarooing) and the smooth fall off of power just before the legal assistance limit of 15 mph is reached (no feeling of hitting a brick wall when the motor stops and your muscles suddenly have to supply all the power).
Although the Roo El is now discontinued there are still some in the shops, but the lowest price seems to be £1200. However if you compare it with other cheaper, heavier, and sometimes much cruder models, you will find the extra expense worthwhile.