The DOD Overdrive Preamp 250 is a 70s-designed overdrive pedal, with a gain knob turning up the dirt and a level knob setting the volume of the output signal.
"Grit turns into more amp-like overdrive, with not much in the way of tonal shift as you turn up the gain"
With the level set high and gain at minimum, you can use the pedal as a clean-ish booster with a semblance of grit to the sound.
That grit turns into more amp-like overdrive, with not much in the way of tonal shift as you turn up the gain, delivering a wide range of possibilities depending on how you combine the two controls. Basically, it adds crunch to a clean amp or drives a driven amp further - which it does very well.
There's more, though: turning the gain knob past vertical and on to its final reaches sees the distortion get brighter and more aggressive as the nature of the diode- clipping circuit starts to offer some of the character you'd get from a fuzz pedal.
There's a schizophrenic feel to this pedal, but that's not a bad thing: just set the gain for the sound you want.