After considering the product features, price, and Marmot reputation for quality, I selected the Helium EQ. I just returned from a three day trip on the A.T. in northern CT and unfortunately the weather was not what I hoped for, but it provided a good trial for my new bag which far exceeded my expectations. The first night was crisp in the low thirties and the following night was in the mid to upper thirties with heavy rain. The first thing to amaze me was the loft of this down bag when I extracted it from the very small stuff sack. The bag was very comfortable, extremely warm, and best of all did not feel constricting. I believe the temp rating for the bag to be quite accurate. I wore a mid-weight breathable long sleeve top and bottoms and needed to ventilate the bag to regulate my temp. The zipper moves smoothly. This bag is a little more costly than some others, but think of it as an investment for a good night on the trail!