Amyrains..I've used the nipple watering sytem but had to stop. My chickens always acted like they were so thirsty when I would let them out to free range. They would go to the nearest puddle they could find and drink, drink, drink. My husband felt they were not getting enough water and convinced me to go back to my old watering method. At that time, I used those plastic waterers that you fill and then invert which I hated. I was so disappointed.
I loved the nipple system. It kept the water clean and it lasted soooo long. Now I use the self watering dog dish that you attach to a hose. It works great for 6 chickens.!
You should monitor them to make sure they learn how to use it by using your finger and making water come out. I'm not sure how well it is with older birds but it took about 5 minutes or less for the chicks to figure it out. Once one gets going on it, the others will soon figure it out. I would check back every once in a while to get visual confirmation that all chicks were drinking out of them.
Also important is height. It's hard to tell for sure in your picture, but it looks rather low. Mine are at a height where they stretch their necks a little to reach. They drink from it often. They're widely used in the industry so it's hard to imagine it being ineffective.
I now have a quart sized "normal" waterer in the coop as well since I have a chukar keeping company with the chooks. The chickens drink from whichever suits their fancy. I once watched one drink from the nipple, then to the waterer, then back to the nipple while I just stood there shaking my head.