I haven't tried KUIU, but have 90% of First Lite' offerings, I couldn't be happier. Their base layers are extremely comfortable, either chasing pronghorn when it's 90 degrees, or last weekend chasing muleys when it was cold to beat heck.
They keep you cool when it's warm, and warm when it's cold. They really help dissappear sweat, don't smell after wearing them days on end in elk camp, I feel they are a great value based on the performance you get.
I would wear their red desert boxers every day if I could afford too, they are unreal.