I have a Harkila Roe Sack which is a very useful bit of kit.
The only problem I found with it was that when carrying it and a shot presented, the strap always got in the way of the rifle when rifle was mounted to shoulder. A couple of times, I couldn't take the shot because of this.
I now carry the sack upside down so the strap doesn't interfere anymore. A simple solution I know. Just for anyone's benefit in case they have same problem.