The only disadvantage I see in a mono is there is no backup if the primary side fails.
That said, early in building my rig I passed on a $200 Mc50. I've kicked myself for that mistake. My 250 weighs approximately 35 lbs. I think the 50 was 10-15. McIntosh amps are extremely rugged. I know someone here dropped one, and it caused a failure...so they're not indestructible. But they deal well with mismatched loads, and they seemingly will take years of being cranked.
Having the stereo amp gives a 2nd channel for an additional cab, or as a backup.
Sorry for the rambling answer, and I can't honestly say whether I've misspelled anything or made any sense. I managed to snag a soundboard copy of the national flu.
"Hi Ho...the Carrion Crow...FoldeRoldeRiddle"