well so far on my experience with mercedes benz i may say not even a single case of the hold function failure for the brake occurs on current GEN model.
the first model which integrated this function however, which is W211 have some sort of malfunction on this, it will come up a message "hold function not available, please refer owner manual" and when this happen there is a higher chance that your ESM( floor shift mechanism) have to be replace.

point A and B is the key different the rest are cosmetic with a batch of sport introduction. and you guys should see A45 AMG (variant 1) coming in by september or october, but unfortunately for the first badge only 20 unit have been order and all sold out.
A250 does feel different if compare to A200 but if you are not a fan of sport tuning you might find the ride is a little bit stiff and hard less comfort compare to A200.