what's the difference between running a preamp pedal vs. an actual rackmount preamp?

What about the mesa boogie V-twin preamp pedal? I think that actually would sound pretty cool using the blues channel into a big muff into the orange.

I know it really just comes down to what I want to do in the end, and I'm most deffinately not going to commit to a purchase until the orange is in hand. Just wondering what you're guyses opinion were.

thanks.