Good app to watch who can call you and blocked the unwanted number. The size of the app is low so it cannot affect performance.
The database of the true caller is quite low security any one can see and edit your number and name. When my name is also edited by some one. You can block any numbers just mark it in the app.
When most of the name is fake. When the app is used, it syncs your contacts and saves them on them database.
If you want make your all contacts private then do not use it.