Fantastic deal. I'd be wary of stacking them that tall given the smallness of the top compared to the bottom of each of those. Go wide instead of tall.
What he said. I'd seen some ugly stuff happen with cabs stacked like they are in the picture. Personally I like the wide setup the best. It just creates this big wave of sound that, if the stage is at the right height, is just perfectly at seated-audience level. Plus it's easier to set up.