It is not a great but good pedal for the money.
The build quality is very good, sturdy metal housing, tactile switch and the knobs are good quality. It is heavy enough to keep itself from moving on the floor, so far found nothing against the build.
Now as for the performance, I am using this with bass (do not know whether its meant for the guitars only or not) and it requires a bit of adjustment for it's lo cut. If the song has distortion and clean both, balancing with the bypass is little tricky; had to cut the treble , lower the middle and boost the bass from the amp side.
My sweetspot is 20% on the distortion, 70-75% on filter and volume and it delivers good level of OD.
To make it even more dirty, I crank up the volume booster on the guitar rather than using the distortion knob.
For the $70, this is a very good pedal over boss but don't expect augilar or TS808 out of this.
For practice and experiment, I'm using it already; for live, I may or may not use this; for recording, nah... I will stick to my aguilar tubes.

Bought it for guitar and doom riffage on a Ibanez RG8.

Bass boost or "Fat" setting is great for standard tuned guitars, but it might sound muddy on extended range guitars.

The fat setting will boost the low end and cut some of the upper frequencies which can muddy up the sound a bit. The stock setting sounds better for brightening up the low strings while keeping the rat growl intact.

I ordered both the rat2 and the fatrat to see which one sounds better for doomy riffs and the cheap rat2 growls just as good as the fatrat with the stock setting.

I dont want a low rumble, I want a growl. I'm returning the fatrat and saving a lot of money.

Not much needs to be said about this pedal because it's time-tested and you know what you get when you buy it.

That being said, the knobs are sensitive so that you can tactfully dial in the sound you're going for. For me, I like a defined distortion so my tone knob is rolled mostly to the left, distortion between 9 & 12 o'clock, and volume at noon (that's up to you). Think Foo Fighters distortion: crisp and dirty. But experimenting with the subtle changes is half the fun.

I highly recommend this for anyone serious about their sound.

I've been through a ton of distortion pedals and none of them had the sound I was looking for. Either too much treble or not enough gain or sustain.

Then one day I played my friend's Rat and was so impressed with its sound. It blew me away, it felt like I finally met my soulmate of distortions.
We jammed a lot together so he left it over my house a lot. At the time I had a big muff and not much money to do anything with (late teens early twenties, when I was going through my Smashing pumpkin phase).
That was years ago, recently I began to play my guitar again after a 5 year hiatus. But most of my stuff was either broken or missing. So I went on a little spending spree and decided to finally pick this up. It was at a great price used. Its funny because I think back when I was a teen I remember this and the big muff being more expensive. Perhaps, I'm wrong or maybe I'm right since the market is saturated with new pedal companies popping up everywhere. I guess the 2008 financial crisis created a lot of pedal makers or maybe its cause of the all the information out on the web now. Who knows?
But all that matters is that even after years of not playing and plugging this baby in, it still feels like my distortion soulmate. And it seems like you can pump some fuzzy sounds with the filter at the right setting.

I have had a LOT of dirt pedals over the years, but always avoided rats for some reason. I am an idiot. This thing is f'ing amazing.