For hunting I think both eyes open is a must! You can see your target so much better, and often your target is in low light. One thing is if you shoot both eyes open you need to make sure you are shooting with your dominant eye....this is very important. If you shoot with the correct eye dominace you can shoot with one eye open or closed.....it really doesn't matter. If you don't shoot with your dominant eye and you shoot eyes open or closed you will and could have real problems. If you don't shoot with you dominate eye, you probably have to shoot one eye closed!

Good Luck!