Agree totally with Bruce that this kit is priced too high for nothing special. If you're going to spend that much for a kit, get a BionX which (I THINK) has a three year warranty or, if they don't have a system for 20" wheels, something similar. The kit you referenced comes with a 36V, 10 a/h battery or
360 watt hours. At 18 mph, flat road, no wind, 180 pound rider, 50-60 pound bike, you would use 20-25 wh per mile with a little pedaling, so good for 15-20 miles.
BTW, installation of a kit is very intuitive even if the directions suck. Do it yourself and learn.