In reply to sebflynn:
I disagree, something to throw on at the belay is better than nothing! Most 100g of more primaloft fill jackets weigh upwards of 600g and are too heavy, bulky to hang of harness. No one likes leading hard pitches wearing a sack, seconding is not as bad, though can still be a pain and awkward.
These pieces weigh sub 400g, pack small enough to hang of gear loop. Last season I purchased a ME Compressor for this very reason, 2 way zip, helmet compatable hood.
Yes, there are warmer jackets, but something is better than nothing!!
Stuart