You may want to also look at the Debaufre Nav B. It is very similar to the Stwoa Airman but comes in larger sizes 44mm and 48 mm.
They are slightly cheaper than the Stowa but their quality is supposedly excellent.
I just received my first order of Lewin shirts. I must say I am very impressed. The shirts are reasonably slim-fitting; the collars appear to structured well and not as hard and stiff as Charles Tyrwhitt shirts and the fabric is impressive. For under $40 a shirt it simply cannot be touched.