As someone who has been Akatsuki longer than pretty much every player in the game, I can confidently say that while +25 to all stats is a strong buff it is one that does not really fit Akatsuki thematically and doesn't help much in situations that you have to face. We are supposed to work in groups of two but that is hard considering the numbers that villages can dish out to counter you.
I have a couple ideas for the ring:
1. The ring casts a map wide genjutsu that reduces the stats of all opponents inside of the map (aka Mugen Tsukuyomi), it would have a certain duration and would cause the map to have a red mist overlay.
2. The ring casts a genjutsu which traps your opponent with you inside an illusionary world (aka Tsukuyomi). Basically teleports you to the map where people usually get jailed by GMs where you can have a 1v1 with the opponent you chose.
3. The rings come in pairs, if the Ring 1 is casted the person that has Ring 2 is teleported to the location of the person with the Ring 1. Allows you to work in pairs and save your teammate when you think it is needed.
4. 10 different rings that each that have different kind of stat buff and a passive to come along with it. (Org rework suggestion) Akatsuki - Suggestions - Nin Online (Idea by @Rumaki)
5. The ring allows you to regen hp and chakra while running.