Pros: gives boost, easy install
Cons: noisy, fine adjustment required, can't go faster than 10mph
The zeta III is an add-on bike motor. So far I've used the Zeta on a 35 minute ride on flat pavement while pulling a kiddie trailer. I could go about 7-8 mph unassisted. To keep up with my bike companion who was going at 9-10mph meant I still had to do a lot of pedalling, but I the Zeta helped make it more enjoyable and I didn't feel like dropping to the ground at the end of the ride. If you go up hills, you have to go at least 6mph or else the motor cuts out. The maximum speed is around 11mph, so you won't get much help if you go faster. I eventually stopped using it because I needed to go faster and it took a lot of adjustments to keep it properly aligned. The Zeta is noisy. It is about as noisy as a large cordless drill. The Zeta uses the same technology as cordless tools. The Zeta works by suspending a belt above the tire about 1mm. When you turn on the Zeta, the belt descends and makes contact with your tire. This is a fairly fine adjustment and may get knocked out of alignment if you transport your bike.