The Mini*Mag is lighter. I like twirling the MiniPro in my hand.
Min*Mag with batteries, 3.8 oz.
XM-3 with batteries, 7 oz.
Easy to replace Mag body using either the Mag warranty or go to your nearest drugstore for a new, inexpensive, body. So I suppose on a whim you could change the color of the body of the light whenever you want to in a minute.
The "wow!" factor of the Min*Mag with a bright light, round and powerful throwing beam still works everytime at work. It still "wows" me. So the Min*Mag is a light that surprises people. The XM-3 looks serious and I don't think the beam "wow" factor works as well for it.
I have the MiniPro in my hand (OK, it is not in my hand when I type) and I'm still waiting for my XM-3. That has to be an advantage.