I too questioned the 20miles @ 20mph. I purchased a 500w 36v kit w/ lifepod 4 battery and performed a test in my area. Hilly New England. I went 20 miles and it was done. I only peddled to help the system up hills to keep the speed up. I am ~6 feet tall and 210lbs. I purchased a new, cheap, mountain bike and converted it. If I replace the knobby tires with Kevlar road flats I might get more range but I have those tires @ 60psi( 5 below max) and only the center 1 inch in touching the road.

I would recommend buying a good system from a reputable company that dose nothing but e-bikes. I was not looking for peddle assist but something that could replace a 50cc scooter. I peddle when I need or want to, less on the way to work and more on the way home.