Is Social.localUser.id unique?

I want to create user connection system with unique id for every user to save preferences. At first time I looked to SystemInfo.deviceUniqueIdentifier but it has problems with iOS 7. iOS7 does note give access to device id and if user updates iOS6 to iOS7, it can create some troubles. So I thought about GameCenter and found Social class reference. But I don't understand, can I use Social.localUser.id in my game like unique user id?

 

Up. Any ideas?

 

16 months later. I am wondering about this as well

 

2 years later..same question....

 

and another 2 years...! also what about userName?

Although the guide says: it is users unique identifier. but in what scope?

https://docs.unity3d.com/ScriptReference/SocialPlatforms.IUserProfile-id.html