just gotten the car 1 week ago. feels amazing and the interior upgrade from the f30 is miles ahead. got it in saphhire black and the paint looks different in every condition (day and night).
driving wise, you really feel the responsiveness of the car and it handles well too. if you want sportiness go for this. C200fl feels more aged than the new g20 in my own opinion.

C200 W205 FL IMO has better head unit & instrument panel compared to 320i. It's bright, colorful, crisp and more customizable than the 320i (330i has different instrument panel). Driving dynamic wise it's inches behind G20 320i but for day to day city drive you won't feel it unless pushed to the limit. Rear bench sitting comfort I'll give it to G20, didn't like the rear bench of W205.

Regarding the mild hybrid in C200 FL, I don't think there's battery involved? It's just an alternator.

Pricing wise, C200 is about 30k more expensive than the 320i (320i can be had under 240k) and without the 5 years free service which worth about 10k if you utilise it up to 100k km. BMW has 5 years warranty too while Merc only has 4.