Re: Volume Pedal or OD/Boost Pedal?
Here's the thing with an EP boost - it's not really a clean boost per se. It does something to your sound, hard to describe but easy to hear and feel.
Most people who use them use them as an always on tone enhancer and then go from rhythm to solo sounds with the volume knob on their guitar.
I've heard but cannot verify that some of the magic comes from the non-linear amplification of the circuit, whether or not this is true I don't know.
The boost adds a texture to your sound that to some people sound like you're 'taking a blanket' off of the amp, but without the corresponding boost in treble, which you can dial in if you like with the EP boost.
The Xotic isn't exactly the EP preamp - but then again there's only a handful of fairly expensive pedals that are. I don't know you'll hear a big enough difference to make it worth while. The Xotic EP Boost from everything I've heard sounds absolutely fantastic, and the one I played certainly was exemplary. As a boost or an always on pedal they're hard to go wrong with.