Milan are clearly not in great condition recently. Their results with Sérgio Conceição so far shouldn't be misleading. They might seem like they are winning most of their games but you must have watched the way they play as well.
They haven't been playing that impressive honestly.

In nearly all of the games they won, they had to make a comeback. Just like the one they made against Parma the last time. The last 2 goals came in the stoppage time which was too extra.

This is the odds for the Derby della Madonnina. Would you trust Milan against Inter now? I wouldn't honestly. Instead, I would go for my mostly preferred betting option recently,
BTTS & over 2.5 goals @2.10.

BTTS much more prefferable to me, though it has small gaps toward total over 2.5. Either of options are good, and worthy to bet.
I was also aware how Milan's performance. declined, but they do have habit to be weak against other serie a club, but strong against Inter. I wonder what thing made it happen, but it seems to me the rivalry between both of milan clubs is the reason.