The Behringer tremolo is very simple to use and does exactly what can be expected. The speed range is pretty wide, and the sawtoothwave/squarewave button along with the depth button makes it easy to get the exact sound you are looking for.
It works both with and a standard powersupply and batteries, even though it was a bit tricky to open it if you are not familiar with Behringer pedals (there are no instructions for this, but a quick web search cleared it up).
If you are looking for a cheap tremolo pedal, this one is definately recommendable.