Here's Keeley's blurb about the rat:
How do you know if you are going to be a RAT pedal fan? If you like a real cutting type of tone, one that sounds like a British type stack of amps and speakers, then the Rat is for you. Delivers classic tones as heard by Jeff Beck, John Scofield, as well as many Heavy Metal groups! Wide Range! Well, the Rat takes some fine tweaking! The controls are sensitive, but once set, it can be tonal Nirvana! Some of our most excited customers are Keeley Rat owners. Also, some folks just don't get it. (Hey, no fault right?!?! Not every pedal is for every person!) I can say, though, that the RAT and TS9 make a power dual pedal setup. For something that has a super sound combined, try your Rat and TS9. Experiment with the order of the pedals. These pedals sound completely different when one is put before the other, and vice versa. Are the magic settings Apocryphal? Yeah maybe a bit! But whence set right... ahhhh you've found the golden needle in the hay stack, mate!