I've used a bag with decent success. I personally don't think a deer is going to be able to tell a big difference at a distance.

One thing I like about the rattle bags is that its somewhat difficult to make them really loud. To me, this may sound more like two small bucks fighting or sparring instead of two bigger racked bucks. I don't think you run the risk of spooking as many bucks this way. When I use them, I try to sound more like a couple of small six points fighting instead of really banging them loudly.