I think Mark nailed it on the use of the bi-pd. You have to load it which usually isn't much more than simply leaning slightly forward on it to remove any looseness. Least that is how mine are.
I use them for hunting quite a bit but we also shoot off of them prior to hunting to verify our sight in as well. Can I shoot as tight a group off of a bi-pod as a bag? That depends on the rifle and load. Usually I can but it isn't nearly as easy to accomplish unless you have been practicing with it for a while.
What I have found is that by using my left hand as that rear bag Mark referred to it is MUCH easier to control things. It does however take some practice to figure out what works best. My oldest grandson has been using one for quite some time. He started out sitting in the woods with the rifle in an almost ready position so all he had to do was raise it to his shoulder and shoot. Now he just accepts it as part of the rifle package and does with it what works best for him.
He used my rifle last year in a sitting position to reach out just over 300yds and drop his first trophy 10 point buck. He was VERY confident and held his left hand under the rear of the stock just like a pro, and when I told him to he squeezed the trigger, and that was that.
