i use it after my main distortion pedal so i use it solely as a volume boost but i have tried to push an amp with it and quite happy with the results.
as a volume boost it definitely has a lot of volume. at 20db max, everyone WILL hear your guitar. at 9 o clock is enough to make your signal jump out of the mix.
as an amp pusher, i usually set the knob about noon or less because more than that the amp will start to have too much bass response.
its a good quality clean boost, no mid hump, no sharp treble jump, just a db increase, and it does it very well. just keep in mind that it is not an overdrive, it will only push the guitar signal louder to the amp.