My flex arrived last Friday. I haven't put any serious time in it yet but here are my first impressions:
Love the new linemans loop locations. The saddle seems to be significantly lighter than my original kestrel. I got the adjustable webbing bridge and I think I'm going to like it a lot.
I'm going to hold off on judgement of comfort until I've got to put a serious sit in it. It seemed pretty comfortable right off the bat but you can't judge performance until you're in a hunting situation. As for the flex section, I don't really see that doing much for me but time will tell. It looks like it will adjust larger easily while sitting in it but going smaller will be pretty tough.