Don't shoot it from max distance into fog of war, drive closer, unload, back off, its highly mobile and quick to fire for that specific reason.
It dies in literally one shot, even shooting it at medium distance is ineffective due to the fact it's scatter was never fixed after the amount of rockets it fired was reduced and they changed how artillery works.
You need to be extremely close in order to hit anything with a reasonable amount of accuracy, and when it dies in literally 1 shot to any explosive weapon and dies easy to small arms fire that's a tough proposition.
It's also very very expensive due to teching. It costs almost as much to get a Panzerwerfer than to get a Tiger.
It also inferior to the Katyusha in every way despite costing just as much.