I actually really like the MAG bass cabs for what they are. They're not top shelf by any means but they're very serviceable. If you were to go for a MAG cab you would want to get a 210, as mixing driver sizes with Ashdown gear is unpredictable at best. Then you could stack vertically, with the ABM on top. That would give you good dispersion and allow you to have the better tone at ear level while the woolier, less defined MAG noise would be hanging out around your knees.
It's by no means the best idea, but it also wouldn't be bone stupid either. You'd probably be definably louder and the vertical stack would provide a better monitor for reference.
Gallien Krueger Club #948 Spector Club #391