I do indeed have a motor I use with both my Bike Friday pakit and my Dahon Mu Uno. It's not a hub or mid-drive (OneMotor friction drive). Since folders typically do better with a little more weight up front, if your system isn't all that heavy (a hub motor of around 3-4lbs maybe) then a front wheel would be fine. Unless you gun the crap out of it going up a hill, it won't be a problem. A 250-350w system is fine up front; if you install a 500+w system it should definitely go on the rear. That said, a rear mount can be fine if your battery placement can balance out the weight of the hub in the back. I would not recommend hanging the battery high off the saddle, which I have seen some folks do. Try to place it on the main tube if possible. Keep in mind if your seat has to drop to fold the bike, then a seat post battery will not be as convenient, either.