The jutsu is a fine addition, gives more survivability indeed in some cases. like when being clustered, if the timing is right I can take the block with 80% defense.
Idk why but at first I thought it was also supposed to ignore slows in the 1.5 second invisibilty.
My suggestion is that false mirror Should ignore the slow, if slowed, for 1.5 seconds and then the slow should come back. its still nearly impossible to leave unleash alive, because in the 1.5 seconds I move 1 tile away and Im visible again.