The GK Deisel Dawg OD has some interesting properties. For individual notes, it can tend to be more quacky and mid-range-y (its three tone controls give you a lot of lattitude that way) - but if you play a double-stop, it generates low-low subharmonics. On doubles, it also messes with the upper harmonics somewhat in the way that a fuzz-octave does - like all skkkxxwiirrshy. Uh - yeah; that's it.
If you crank-up the gain, it can also do heavy distortion, and if you do that while scooping the mids and raising the highs (called "edge"), it gets a real 'metal'-tone that I'd think would be great for guitar.
I must admit, though, that I rarely use it alone; I usually use it to drive an ODB-3 with (the Dawg is running a light overdrive, while the ODB is cranked). That sounds killer - but my full, all-out high-gain sound includes a CEB-3 (chorusing only high-freqs) and an Xciter between them.
Where I don't want the D.D. is for a synth tone. Then I run CS-3 compressor to OC-3 octaver (in poly mode) to the ODB.
I use the ODB-3 by-itself, more than I run the D.D. by-itself - but Dawg into ODB is pretty amazing to me!
Joe