Hyperfly rashguard size question

i was thinking about buying a rashguard from hyperfly but i've always been told that for clothes in general US sizes are different than europeans, so i would love some feeback from people who own some hyperfly rashguards.
in us measurments i'm 6 ft and 162 lb and on the hyperfly size chart for chest size i'm right between an M and an S, could anyone tell me which one should i get?