More powerful pedelecs which are not legally classed as bicycles are dubbed S-Pedelecs (short for Schnell-Pedelecs, i.e. Speedy-Pedelecs) in Germany. These have a motor more powerful than 250 watts and less limited, or unlimited, pedal-assist, i.e. the motor does not stop assisting the rider once 25 km/h has been reached. S-Pedelec class e-bikes are therefore usually classified as mopeds or motorcycles rather than as bicycles and therefore may (depending on the jurisdiction) need to be registered and insured, the rider may need some sort of driver's license (either car or motorcycle) and motorcycle helmets may have to be worn.[14] In the United States, many states have adopted S-Pedelecs into the Class 3 category. Class 3 ebikes are limited to <=750 watts of power and 28 mph.[15]
An electric bicycle is a bicycle with an electric motor used to power the vehicle, or to assist with pedaling. In many parts of the world, electric bicycles are classified as bicycles rather than motor vehicles, so they are not subject to the same laws as motor vehicles. Electric bicycles are one type of motorized bicycle. However, electric bicycles are defined separately and treated as a specific vehicle type in many areas of legal jurisdiction. 

In general, more expensive bikes are better. However, this is just a trend. E.g. the "Kassensturz" Consumer program from our state TV found in a 2012 study confined to an engineering school, that "Supermarket" bikes, e.g. the 1400 CHF (1200 Euro) "Leopard" bike from COOP did very well. Evaluation is "good" (almost the same as the three times more expensive 25km/h Stromer). They also pointed out a very bad model from a discounter. In other words, you can find good cheap models, but read the tests first.

Simple, convenient, cheap, and economical—bicycles are one of the world's favorite forms of transportation. But they're not for everyone. They can be hard to pedal up and down hills or with heavy loads, and elderly or disabled people may find them impossible to manage. In the last few years, a new generation of electric bicycles has begun to revolutionize our idea of environmentally friendly transportation. These new cycles have all the convenience of cars with all the simple economy of ordinary cycles. Let's take a closer look at how they work.