I think these are the same as the open-ended one on the OR Zealot jacket? If so, some cautionb is needed. We found that while the zip runs freely enough, and is moderately water-resistant, threading the (open) end together to start it is an absolute PAIN! You would not want to have to do this in the rain with cold hands of gloves.
However, if you want to use a single-ended one on the beak, it should stop most of the water and work reasonably well.