His time at Leeds is the best indicator to go off considering why you'd be hiring him? He follows the Red Bull game plan, he doesn't have one himself.
Also a little off topic of how he would do but the signings aren't his signings. I have no doubt they would run them past him but he really doesn't seem the type to cause any issues. Victor Orta went to Bielsa with multiple players and he refused a lot, I can't see Marsch doing that. Some of our signings have not been great. Adams and Wober have been great, as well as Gnonto however that transfer wasn't as straight forward, we weren't even supposed to be signing him when we did. The rest are very hit and miss.
Also the let down by sloppy goals is a massive understatement. Those sloppy goals happened week in and week out, they were a result of the tactics Marsch implemented in our team, everyone in the ground and social media could all see it but nothing changed.
You're in a very similar position to ourselves when he took over, yours looking a little bit worse than ours did. Under Marsch we went down the table.