I've got a Yellow Spiral - haven't done a side-by-side in a while, but I recall that the MBD1 at lower gain settings with the Shift down can be somewhat close to the YS with the gain maxed (but MBD1 with the gain trim cranked can get way more brutal) and the Girth at max. Interestingly, I could never get the super distorted sound like this video ). While MBD-1 can go from light OD to crazy distortion and even fuzzish tones with the Depth maxed, the YS seems more like a light OD that also functions as a tasty boost. I've also tried it as a Preamp - and certain boosts can sound good slammed into it (Nunez Dual Range boost for example)
Thanks!