My doppleganger warlock took this as her 2nd level feat (1st level was Ranger multi...it worked storywise, I didn't realize how powerful it was though until play, a lot more than StC). In two sessions and 7 encounters, I've used StC once. Of course, that means I only missed once. So while it's nice insurance, I'd hardly call it overpowered, and it sure doesn't turn her Witchfire into an at-will. The DM agrees...and maybe feels sorry for me being a doppleganger; great for RP, but not a combat optimized race, for sure.