At the moment Mercedes only have a 5% stake and the Team principle of Mercedes F1 team is also believed to have a significant stake, so it is hardly a complete takeover.
A closer link to Mercedes can only be a good thing for the Aston Martin. I have had a DB9 a Mercedes C63 Cabriolet and now a DB11 V8 with the AMG V8 engine. There is no doubt (apart from low speed brake modulation) that the DB11 is much better engineered even if it is not as good looking as the DB 9.The engine and driveline is a huge improvement on the DB11, as is the electronics.
