Before I got my S10 EV back in July I had ordered a DX bike kit from Zap. It's been on back order since June and it finally came while I was in Boston. The DX is a dual motor 12v kit that you simply bolt onto your existing bike. Goes ~18mph with a range of about 15 miles depending on how much you pedal. It has a regenerative mode which is suppose to help charge the battery when you coast downhill. The motor will assist you as you pedal or you can just sit back and let it do all the work. Going up hill you have to pedal but the ad said... "Lets you take hills like an athlete." If the battery runs down you can just pedal like a normal bike.
The motor mounts to the seat stay with a metal plate. Took a bit to get it adjusted so that the motor will try to 'climb' the tire as it pivots into the tire. This increases the motor's grip (friction) on the tire as the motor shaft rotates. If you pedal (or coast down hill) faster than the motor is turning the tire will push the motor away. Simple but effective design and seemed to work well. There is a lever to lock the motor against the tire if you want the motor to do all the work.
I wish I could say it worked 1st time, but it didn't. I hooked all the connectors up, charged the battery, but nothing happened when I pushed the handle bar mounted switch. Forward for high speed, back for low speed, and center(auto-return) for off. Took me about another hour to debug the problem.
But after getting the 3 pin connector right, I when for a test ride and I have to say it easily pulled my 225 lbs along at a faster than I pedal normally pace and climbed reasonable grades (small hills) by itself. For sure I will have to pedal some to get up any real hill with the motor doing most of the work. Still too early to judge the range. But I have to say that this kit can take the hard work out of bike riding, while still giving you some exercise. If getting all hot and sweaty riding to work is stopping you from doing it this kit could solve that problem.