I love almost everything arcteryx, but this harness is way off the mark for me.
A: Yes. Size up. I'm a medium in everything arcteryx (including their harnesses) and the medium is too small for me.
B: Arcteryx shaved a lot of weight off of this thing. Major casualties include two gear loops and the absence of a a chalk bag loop ... which is more than mildly irritating. I know this is designed to be outrageously light, but arcteryx used a silly piece of fabric across one of the leg loops for the sole purpose of putting their logo in it ... this could have easily be eliminated in favor of a chalk bag loop. This is almost a deal breaker for me. Perhaps that's silly. But adding another belt across your stomach for a chalk bag is just another thing and adds a "lot" of weight.
If you get the right size though ... the harness is very comfortable, very light, and very breathable.
Not for me though.