Got it, tried it on and it hasn't disappointed. Glad I went for a medium, in the end. I'm 5ft 9", slim/athletic build - was a bit worried I'd undersized as my shoulders are quite broad so I was concerned it'd feel restricted across the pits. Seems fine though - I wanted it to sit quite short, the same fit as the Rivet and Hide model on their website.
Really happy, despite the cost of import