Summary: It adds a lot of low-end (bass tones) to your guitar signal, and it can get really noisy. However, it seems to go well with single-coil pickups (at least much better than humbuckers).
I wanted to have a pedal in front of my amp that has overdrive/distortion characteristics, specifically to use with humbucker pickups. Since this is a cheap option, and it has relatively good reviews, I wanted to give it a try.
First of all, Low/High switch doesn't change too much if you are connected to a cranked amp.
The pedal is quite noisy (both with clean and cranked amps), especially if the gain and level knobs are beyond 12 o'clock.
The worst part for me is that it adds a lot of low frequencies to your guitar signal i.e., it adds lots of bass tones.
When I tried it with humbucker pickups into a Marshall DSL, due to the nature of humbuckers, the bass response was awful such that I couldn't even tune it with the EQ of my amp.
Then, I tried it with my telecaster (single-coil pickups) into my Fender Twin. I liked that sound since it added a bass response on top of the brightness of my tele. However, I didn't plan to add a pedal to my 'clean' rig. So I returned the item.