Looks like Samuel's mom beat me to the punch!
I can only answer part... I don't know about restricting to 6 oz. Hopefully someone else will come with some good advice about that soon.
As for "will they eat more?" the answer is yes, generally. You're right: they don't have to work for it as had from a bottle, and it's a novelty to your LO (since she doesn't get it often). In addition, if she's trying to comfort suck, that means that she's taking input from the bottle simply because it's there. If she's comfort sucking at the breast, she can regulate it such that she doesn't take in much but still gets to comfort herself. HTH.