It's now or never for him, he will never test himself at very top level of club management if he didn't take this risk.
I am not sure that is true.
On the one hand, Bayern are in relative disarray, with massive pressure to right the ship, he isn’t a “big” manager signing, and has a connection to a despised rival, so he is likely to get very little leeway from the fans or media.
On the other hand, perhaps the current dysfunction and underachievement at the German Rags will give him some cover and make his management seem stable and positive by comparison. If he wins the league next season (I think that is more likely than not), he can take credit for the achievement and build from there.
I still worry this is too much, too soon, and will actually end up knocking his career back further than just staying with Burnley to fight for promotion back up next season or taking an offer from a lower level Premier League club to gain experience and demonstrate his approach can work at the top level, before moving up the ranks.
Then again, I always favour the slow and steady approach, which is probably why I am discussing this on an online football forum rather than furiously watching opposition tactical videos put together by my crack analytics team ahead of my club’s CL final.