[soMa]

It's not making them useless its adding an exact counter that will take skill / timing to use. Making it cheaper than the invis potion would be better but having it cost the same amount to make as an invis pot would be ok to.
This stuff ad's more depth to the game.

Eventually there will be so many people crafting every single thing that if there isn't variety in items the economy will hurt.(at least that's how I see it)
So these ideas that drive pvp at the same time drive the economy. (making crafters have more worth and making them needed)