This is a superb tremolo pedal: [1] Its dials allow for enormous control of the effect. [2] It's very sturdy--an often-noted feature of BOSS pedals. Further, [3] it's utterly easy to use, [4] allows for both 9v battery and power supply/adapter operation, and, most important of all, [5] it delivers beautiful tremolo. (Note: It comes with a 9v battery installed, but it does NOT come with a power source/adapter.) If the price is more than you're willing to pay, consider the DANELECTRO COOL CAT TREMOLO. This also delivers good tremolo, but it does not allow for as much sound-manipulation as the BOSS product; it's still quite good, but the BOSS takes the prize. I paid about $75 for mine and have zero regrets.