Overall, this is a great base layer for cooler weather activities. I've used it for running around 20 degrees and it's pretty warm. It also acts as a good layer for cross country skiing. I love the bigger pocket on the back. I can actually fir an iPod/keys/ID in the pocket (unlike other shirts). I also like the reflective details.
I've used the beta 1/4 zip for running in cold weather. It keeps me pretty warm. It's comfortable down to about 30 degrees or so. Anything under that is definitely pushing it and would require another layer. There's a pocket in the back big enough for an iPod and ID card. I also really like the purple color (my favorite). Overall warm base layer for a nice winter day!