Yes, the DS-1 is a great little distortion pedal for a tube head that has problems geting good distortion/crunch on it's own. It can be used to overdrive your tube amp in a good way.
It's kinda noisy, and a little hissy (not very articulate, more of a blanket white-noise type distortion).
It'll load up the signal strength and, if you've found the right settings, will give you a nice blend of sterile and noisy diode distortion and warm and fuzzy preamp distortion.
You might need to fool with it a bit, but level slighly past 12... almost at 1, and distortion between 1 and 2 o'clock...
I've been using my MT-2 lately, but just on my practice rig.