is Master-Master replication ok for me? I have two separated locations connected by a not too reliable VPN. I have a common system that depends on MYSQL that read/write tables. 
Will master-master replication keep both locations in sync?
I don't care that tables might not look exactly the same in time on both servers (for example, rows on both masters when VPN fails, might get a different order after both locations write transactions...)

Note: Not doing auto-increment / offset settings
I have a third party app that is using a master-master MySQL system and if  your network/communication is not good you may have some issue with your replication.

Types of errors you may encounter is 1062 (duplicate key).

Right now to avoid this error we put it in the slave_skip_errors in themy.cnf file.

Also if your network/communication is not good is not good, your instances may keep and failing back and forth.

It can work but you will need a lot of fine tuning and monitoring.