My regular mechanic is suggesting switching to mobile-one.....I have been using Castrol full synthetic. 2011 clubman just turned 100k. Any comments. tks

 

I've been a M1 user [10w30 & M1 filter on a 5k interval in the Justa, based on what I've read on here] for years across multiple cars with no complaints. I know the dipstick mount recommends Castrol, but it's not as 'off the shelf' accessible.
Prior owner was running Motul, but it's even less common on the shelf, from what I've seen.

 

Is he getting a kickback for the rec?

Can't see any reason to run Mobil 1 over Castrol.