It outranges ISG guns by far, Ostheer mortars don't stand a chance and it can not be countered when placed out of your reach. The result are 2, often 4 mortars shelling the frontlines and stopping every advance towards the VPs.
The main problem is how they can be placed so far behind the frontlines that their supposed counters are not able to reach them. Despite firing on maximum range they remain very effective thanks to their numerous amounts. It's also not uncommon to cover 2 VPs with those emplacements.
Unlike their counterparts - the ISG and mortar - they can scale well into lategame since rocket artillery will hardly harm them.
yap,ive posted this before.