Painkiller Illrigger questions

I'm about to start a new character in a running campaign, but I don't know if I understand all the class features correctly:

The invoke hell feature gives 2 options. Grand strategist and Punishment. Grand strategist requires no action, does this mean I can use it only on my turn as a free action or at any point during combat? Punishment requires only a reaction when taking damage. Can I use it on all kinds of damage and just blast that straight back? I don't see anything in the app limiting it's uses like once per short/long rest, up to proficiency bonus or class level. Seems kinda broken.

Would love it if someone could way in on this.

But you only have one invoke hell to do either effect, isn't it?