Autoglym products, when used properly, can be very good.
SRP has come out on DW tests as one of the best for polishing by hand. AG HD wax is also highly regarded.
I love their fast glass and glass cleaner. Their bumper care one is okay but by no means perfect. You have to remember that AG is for the likes of the general public. Was having a chat with my boss and when he had a Porsche, he thought using AG meant you were the don!
For those i who are professionally/semi-professionally into detailing, there are millions of other products that do a far superior job. For joe public, it's fine.
Endorsements by the likes of Aston Martin IMO don't mean anything - just that there's been a deal done by them.
As for your mate, if he's any good, he should be able to give you the pros and cons of using AG rather than just sh*tting all over it. I've heard semi-pros talk in a similar way about Dodo Juice.