Hi,
One additional major difference is in how the oline alter table propagates through replication.
With online DDL, it just serializes like any other statement in binary log. To the best of my understanding it makes for a blocking statement on slave.
Which means this is all fine all master, but then you will have to forget about your slaves for a couple days… A solution for that would be to issue independently with SQL_LOG_BIN=0 on all hosts.
