Any player can use these stones. They can take skills that are stored on the Soulstone off and they can put a skill they no longer need or want on a Soulstone.
We are a small server and I found this came in handy. There were times that players gained a skill and then changed their mind and no longer wanted to go that direction. They can instantly remove the skill this way, or another player can pick up perhaps one they are lacking.
I have a house that has the fully customizable vendors and other special things in it along with these Public Soulstones.
We are a work for your skills server with a 900 cap and 250 stat total. I don't see any issues with these causing imbalance.
Anyway, change, use, do as you wish and enjoy!