Very, but the problem I see is that it actually tires you out, I recall kakashi explaining and saying how you place all of your chakra some where and run as fast as you can while swapping with an object(needless very needless) within like a second..Subsitution no Jutsu
Flames that last forever it used to be a god in part1 when itachi attackedAmaterasu.
Very underated seeing as to how sensing is only among a small group(until it was asspulled to like everyone O_O)transformation jutsu.