Using the T-Rex Engineering Bloody Mary is a really easy task as the pedal is easy to follow and has pretty basic parameters. The pedal has knobs for gain, level, low, mid, and high, as well as a button for body. I've never had too much trouble using this pedal because it has similar parameters to other distortion pedals out there. Even if you aren't too experienced with distortion pedals as long as you experiment and try things out you should be able to get a handle on this pedal pretty quickly. I haven't seen a manual for this pedal, but you shouldn't really need one anyway as the pedal is easy enough to use on its own.
Out of all of the T-Rex Engineering distortion pedals, the T-Rex Engineering Bloody Mary has the most gurth and is best suited for heavy rock music. I have used the pedal with a '76 Fender Twin Reverb amp and a Fender Stratocaster or a Gibson SG for the most part, so I'm getting a pretty accurate portrayal of what this pedal sounds like. I especially like using this pedal with the SG as you can get a really fat tone that is great for harder rock music or if you are just looking for a really heavy distortion rhythm or lead guitar tone. While this pedal isn't all that versatile and is rather limited in the types of tones that you can get, the sounds that you can get are pretty great.
I've been using the T-Rex Engineering Bloody Mary for about a year or so and I would definitely recommend it to the group of players who are looking for a really fat distortion sound for playing harder rock music and metal. It is good for other genres too, but I have found it limited in its use for other genres. The price isn't all that great but is worth it if you are looking for tone like this...This pedals is definitely worth checking out for those who are looking for a heavy distortion pedal.