In reply to UKC/UKH Gear:
I have the Atom SL Vest and really like it for mild weather activity that can get a little chilly in the morning and evening. For typical US not-really-alpine summer conditions, I think that a long-sleeve sun-protection hoody, the Atom vest, the Rab Vapour-Rise Flex jacket, and a goretex shell for wind and rain protection will work really well in a combination of conditions when generally mild weather makes breathability during activity one of primary concerns. Add the very light and compact Mountain Hardware Ghostwhisperer down jacket to the pack and I should be ready for the kind of sometimes-intense afternoon summer storms at altitude that can blow up in the Tetons and Colorado Rockies.
Caveat: since the vest is very new, I haven't tested this combination in the summer conditions mentioned, but rather in relatively mild winter conditions that I believe are equivalent.
I might add that the vest stays tucked in to my harness; hem length is not a problem for me.
Post edited at 04:13