I played around with this in singleplayer, and it works surprisingly well.
There are a few things I want to give input on:
1) The mortar system is fairly robust and easily deployable. IMO the damage values could be tweaked to do slightly more damage, and the damage radius could be upped as well. Any HE mortar shell is more than enough to kill a target within a 5~ meter radius, although this is not the case with the default mortar config in the mod. Overall, the rangefinder in the mod works flawlessly paired with the mortar tube and range card and it's pretty enjoyable.
2) I don't think every ARF or Heavy trooper should have access to it. The system is pretty robust as mentioned so giving it to every Heavy or ARF trooper would be overkill. This is one of those things where you either need to give it to a select group in one battalion or spawn it in for events only (similar to the AV-7).
3) I don't understand the people saying not to add a training. I understand training can be tedious but you are literally giving someone a tube that shoots explosive shells and asking for them to not be trained. What could go wrong?
Edit: I forgot to add a +1. I like the idea, we just need to think about the right way to implement it