I have a DM4.
It is pretty cool to basically have 4 extra channels.
I like the Tubescreamer setting. I use it a lot.
I have also had trouble with one of the switches on mine. Pushing down the 2nd to the left button results in either: the 2nd channel turning on, any one of the other channels turning on, multiple lights turning on, or nothing at all.
I got it on sale back in high school. If I didn't already own it, I would just buy individual pedals, but since its here, I might as well use it.
Its probably also worth noting that you have to adjust each channel's volume when you change the volume of your amp or some will be louder than others.
Despite how critical I've been of it, its still a pretty cool pedal. But I wouldn't pay full price for it.