Pros: cheap, fun to ride, good for climbing hills
Cons: heavy, short range
I purchased this electric bike in the hopes of making my 13-mile commute to work a bit easier. It was the cheapest electric bike I could find. At ~$350, it's cheaper than a lot of non-electric bicycles. The Mountain Trailz can be a really nice bike, depending on your needs.
The bike is designed as a pedal-assist, meaning you pedal and use the electric motor at the same time. It's basically a mix between a bicycle and electric scooter, and the motor makes pedalling much easier, particularly when going against a headwind or uphill. It's very simple to use - just attach the battery, flip the power switch, and use the throttle as much as you'd like. The bike also has 7 gears, which is plenty because of the electric assist. I usually only used 3 of the gears.
It also comes with a key with which you can lock the battery in-place on the bike, or you can also detach the battery and take it with you. This makes it easy to recharge the battery anywhere (charger is included).
The only problem with the e-Zip is that it's heavy and doesn't have a very long battery range. The manufacturer estimates the range at 18-25 miles, but a more realistic estimate is 10-15 miles, and that's with both pedalling and using the electric motor for the entire trip. Since my commute was 13 miles, the battery would often die out about 3 miles before I got to work, and since the bike is so heavy, it's a lot of work to pedal it without the electric assist.
One other negative aspect is that it's rather difficult to change the back tire if you get a flat, because the electric motor is attached back there, and there are no instructions for this task. It took me quite a while to figure out how to replace the tube, and once I did I put in a nice puncture-resistant tube so I wouldn't have to worry about it again.
However, all that being said, if you won't be riding this bike for more than 10 miles before recharging it, it may fit your needs. It's a lot of fun to ride, and particularly useful if you're biking in a hilly or windy area. Of course, the more hills you climb, the sooner the batteries will run out of charge. They only lasted me 10 miles on the way to work but all the way home because my office is about 60 feet higher in elevation than my house.
The cruising speed on flat terrain with the e-Zip was about 16 mph. In comparison, my road/mountain bike hybrid cruising speed is around 14 mph, and my road bike is also around 16 mph. So it's not a super speedy ride, but the main purpose is to make pedalling easier.
It's also important to recharge the batteries ASAP after a ride in order to maximize the lifespan of these sealed lead acid (SLA) batteries.
In short, the e-Zip is a cheap alternative to an electric scooter with which you can get exercise while not having to work too hard to pedal, and have a fun time doing it. As long as your trip isn't too far, the e-Zip can be a nice, cheap, and fun option.