He would improve us because he is better than all our current options.
And if you think "he's not good enough for them, how is he good enough for us?", does that mean players like Szczesny, Gibbs, Sagna, Arteta, Cazorla, Walcott, Podolski and Wilshere are not good enough for us? Because neither of them would start at Bayern. Or does it only apply to Mandzukic?