Dude don't go everywhere telling that Naruto is using FTG without seals.Naruto doesn't need the special seals to teleport and I guess that has to do with the power of the nine tail demon and his genetic instinct of reaction. Minato probably knew that it required something special (nine tail demon fox) to perform his FTG without marks, thus the reason he sacrificed his life to give naruto this new power just like itachi sacrificed his to give sasuke new powers.
Like father like son.