Scott, the vegetable tanned goatskin used on the Mark 31 is IMO every bit as nice as the goatskin used by Aero, which is really saying a lot. The chrome tanned goatskin used on most of G&B's other jackets is completely different than the veg tanned goatskin used on the Mark 31, and you will see what I mean if and when you have the opportunity to compare the two together. Enjoy your visits to San Diego, which might be the nicest all around city in the US. You will definitely enjoy a visit to G&B!
Fanch, I own a G&B Navy G-1 and a M-422A. I was recently sent a leather sample of their veg-tanned goatskin and I don't see much of a difference at all. The grain is a little more pronounced than their chrome tanned but nothing dramatic. The thickness of the leather is actually a little thinner than the chrome tanned goatskin sample I have. I was expecting the veg tanned goat to at least feel stiffer than the chrome tanned but they both feel exactly the same! I was actually quite disappointed. I was expecting to see a big difference.