Oh it adds plenty of weight. A buddy of mine had a similar replica and let me use it a couple of years back. I thought it was heavy and gave it back so I didn't hurt myself. After a few shots in the rain today, I was convinced this one is also heavy. You would not want to give a huge heave on this bad boy! I may have the main shaft a bit too long. I am contemplating making a similar version with a shorter wooden shaft and then do some comparison shooting. I also plan to make a third that has no stone at all and see how that all works. After reading up on Indian Knoll's atlatls I am convinced this the purpose of a bannerstone- on the atlatl shaft. Now were they just for show or were they functional is another question. Bob Perkins posted an article on line a few years back that suggests that wings help reduce the swishing noise volume and sound frequency so it is lower. A silencer of sorts. Stealth technology according to him.
As heavy as this feels I have come to realize there is a lot I do not know. I made a replica of an atlatl found at Council Hill Nevada and came to the conclusion that it was not a very good thrower. It was about 20 inches long but was not more than 7/16" wide and the spur was terribly short. My darts would barely fit on the spur. Then a fellow atlatl enthusiast came to an event with these little 3-4 foot long darts. They were almost arrows, and they worked GREAT in a smaller, thinner atlatl. I tried the Council Hill replica and it was a dream boat to use. The atlatl was fine. I just needed lower mass darts. My six feet long river cane darts were mammoth in size by comparison. It never occurred to me to adjust my dart. I will see if I can dig up a photo of that thrower to post.
Does this winged bannerstone atlatl seem heavy? yeah. Do I understand why? no. Will I? If I keep workin' on it I might.
Feel free give me some of your thoughts. I love the exchange.