Plattenhardt has been a consistent 6.5-7/10 week in, week out Bundesliga LB for 3+ seasons. He's tremendously fit, gets up and down, takes good set pieces but he is an average defender and more relentless than creative in open play. The words 'steady' and 'solid' featured a lot in the e-mails I got.
Philipp Max was an incredibly talented young prospect who hit a wall, got transferred to a smaller team and finally emerged and played like the player people thought he would be last year after a couple of average seasons with some consistency and injury issues. He's a superior footballer in open play, an attacking threat in his own right, creative and dynamic but he's also only an OK defender in common with most modern fullbacks. Big upside but more risk as would we get the superstar from last year or the rather disappointing version prior to that. The Schalke fans were both particularly cautious as he ultimately fizzled out with them.
Given we have the insurance of Baines at the moment and a promising young player in Robinson who has grown on loan at Bolton and begun to establish in the US team perhaps Plattenhardt is a better fit as a reliable, consistent, plug and play lower risk starter but Max, if he panned out, would be a difference maker.