FET boosters are a bit of a new thing today. In the past, people have been experimenting with FETs and utilizing them for diodes in the clipping section for awhile. However, some people started taking the old school approach and trying them as an almost quasi-treble booster style pedal. What I mean by that is, they simply have a knob that allows you to dial in the amount of FET boost you're looking for, and it's a pretty ingenious way at helping give you a great sound without much actual knob fiddling. The pedal features only one knob, and honestly, that's all it needs.
There's not much going on here, and that's a good thing. There's no real need to be switching all kinds of different resistors/caps/diodes in and out of the signal path because it's already great as it is. All you need to do is dial in the amount of FET boost you're looking for, and the pedal will do the rest of the work for you. It's a small pedal, and it'll fit on pretty much any pedalboard out there. I'm a big fan of these smaller pedals because I need as much real estate on my board as possible for other effects. The pedal is also true bypass, so there's no need to worry about your tone sucking when it's turned off.
There is one knob. Turn it up for the effect to be more prominent and turn it down for more subtly. It's really that simple. Most people are wondering exactly HOW is sounds. Well, imagine a thick, juicy steak. That's really what FET boosters are like. They add this warm, complex and fat sounding boost that is awesome for mid gain. They can work on high gain as well, but once you start compressing the tone real hard, the effect gets to be a bit less prominent. You can use this as a booster for your clean tone, but you'll probably want to watch your volume levels just in case.
There are a few FET boosters out there today, and this happens to be my favorite pure FET booster. I normally enjoy FET diodes in my signal path when I'm boosting mid gain amps as they add tons of character, but I don't use them that much when I'm playing death metal and the such as the amps are already so compressed that this just doesn't add anything extra to the tone.