I bought this when I was on a tight budget to get some dirt for my bass. I couldn't find a dedicated bass distortion pedal in that price range that I liked, so I tried this out.
It works perfectly fine, and has more than enough gain, without losing too much low end, which is always a risk when distorting a bass. Just add a bit low end on your eq and you should be fine.
Other than that, the build quality is really great. Not made of the same flimsy plastic as some discount brands tend to, this is build like a small tank, so you don't have to worry about breaking it.
While I havn't tried to use it with a guitar, I can certainly recommend it for bass, especially if your budget is tight.