I built two of them in a 2v2 last night. Our opponents countered with the Mortar HT and it's incendiary rounds. This was an excellent counter, and they wound up winning the game. We had to change up our strat to get the best of them in the rematch.
Interestingly enough I always found the 120mm to be very accurate and powerful, but I never saw use in building more than one of them .
So I guess it's finally time for me to try out Festung Support, although I hate everything else this doctrine brings...
Is there any viable method to actually destroy the mortar? I often manage to decrew them, but since they're always setup in "enemy" theritory they ar soon recrewed by cheap conscripts and the whole thing starts for a new.