Does SystemInfo.deviceUniqueIdentifier really need permission in Android?

I am using Unity 2017.1.1 for my project. I want to record user unique ID to track download record so I used SystemInfo.deviceUniqueIdentifier. However, I found on the Internet that this variable needs READ_PHONE_STATE permission on Android 6.0. I tested on two phones with different brands and both are in Android 6.0.1. The app did not ask me anything about the permission, and it got the ID without any problem? So I want to ask if we still need to ask the permission, or that is not necessary anymore?
AFAIK it should work without READ_PHONE_STATE since if the check fails, it just uses another way.