I just got my black Jumacse in small! They came quick... quick like a cat. Ordered late Thursday evening and received them today.
The thing is absolutely beautiful. I've seen the heather grey in person, and I think the black is the second nicest after the almighthy white Jumacse. (if anyone wants to trade their small white for my small black, holla!
As everyone has said, it does run tight, but I think it is made to be really fitted anyhow. It is indeed smaller than the Jubetwo in the same size. All other proportions are about the same (sleeve length, body length).
Although, it does fit tighter initially b/c of all the extra lining and slim-cut. I think it will stretch pretty easily over time. Far more than a Jubetwo would anyhow. I don't really recommend sizing up unless you want some super long sleeves, etc.
Just my opinion though.