I think a Gustin small is very close to an Epaulet medium. I own both and think both fit well. Epaulet shirts have a bit more taper thanks to the darts but they are the same in the chest and shoulders.
I'm actually pretty excited about this new line of products and, if I'm able to make it up to NYC for the launch event and get fitted by Mahon himself, am going to try to get in on the first round of orders.
Did the sizing advice work out for you? I'm a true US9D but I'm a little nervous about a UK7.5 as opposed to a UK8.I'm just going to clean them with AE conditioner/cleaner like I use on all of my calfskin shoes.