I have an Inquisitor who is heading for the Hellknight prestige class and for story reasons I don't want him using any kind of plate save for the hellknight plate. The presence of the feat is less to wear any heavy armor and more gaining the right to don the suit. I'm a little confused as to when hellknight plate is available though. The class says that at 2nd level they gain the right to wear it and the bonuses start kicking in, but I also see on other characters and PFS where it can just be picked up. Probably overthinking it a bit but did want some clarification on this point for the character.
At second they gain the 'right' to wear, so if other Hellknights find someone impersonating a Hellknight, they might suffer some retribution. PFS is its own monster.