My ebike is a regular Mongoose mountain bike from Walmart with an electric hubmotor kit that I added.
I got the brushed motor kit from Wilderness Energy, though there are other places selling other kits, some cheaper and some much more expensive.
With the "extended range" battery pack (3 12 volt 12 amp hour batteries in series) I got around 10 to 12 miles per charge when it was new, now the batteries are 3 years old and I can only get about 4 miles per charge. The more expensive brushless motor claims much longer range.
I am about 210 lbs and we have several small hills.
On fresh batteries I can ride all over town, even up all the small hills without pedaling.
Everything seems quite well made, though the charger that came with it burned up early in the second year and I had to buy a new one.
I like the kit because I can put it on whatever bike I want, I have changed bikes once already. It's nice not to be stuck with an uncomfortable bike.
With a fresh charge on the batteries I have hit 23 mph on a flat paved straight road.
That's without pedaling.
I ride it to work and back every day, as well as around town for light shopping etc.
I'll be happy to answer any other questions, I'm a bit loopy right now, been up most of the night. Sorry if I sound a bit disjointed.