Love my Dinotte's. I run 2 200L's on my bars (more expensive than the Mininewt) I have hit a max of 43mph so far on a winding downhill on an unfamiliar road without trouble.
http://trail.motionbased.com/trail/activity/3577489
I can't say that I notice any handling issues with the battery packs. They weigh very little.
-D