1 - The mobs down there having upwards of 400 damage is more than enough to balance it out. And I can't even survive with my hp-less mage of level 50+.
2 - No, I think it's stupid. Yes the lava burns you after a while is OK, but why won't the potion kick in? It's what the potion is used for after all. If you say it's too OP, might as well ask Red to remove it from the vanilla, because "hey Red, all you need to dig hellstone is just some cheap evil pickaxe and obsi pot, can you remove the pot?"
3 - It already takes so much trouble getting the pick necessary to mine the hellstones with the
mod.
4 - Meh, probably just me. I was not pleased finding out I wasted materials for the potion. I guess I'll just raise another char to a good lvl to mine the stones instead.