If you want to use it, go right ahead. It's your flock and you are the one who should decide what's best for your flock. However, if you do decide to use it, please make sure they have access to clean, fresh, unaltered water as well.
My experience with ACV was pretty simple. I started out using it faithfully when I first got chickens because people I looked up to said it was best. Then I ran out of it and just kept forgetting to pick up more. Well, after almost 5 years I didn't notice any difference in my flock, egg quality, overall health, or anything else. Personally I don't want to mess with their own bodies' ph so I'm totally fine without it. And I think all of those things - all the additives, the DE, the pumpkin seeds and such - just give us a false sense of security and we become less diligent than we should be. "My chickens won't get mites - I use DE." "My chickens won't get worms - they eat pumpkin seeds and have ACV in their water." So we don't check things over as carefully as we should and the next think you know what could have been a minor problem has blown into a full blown infestation or overload that will take weeks of hard work to get under control. In my mind there simply are no instant miracles.