@skytrex I believe the only difference from them is that the master password can also do what the memo key does (which is send encrypted messages, which is a function I don't actually think it works, or at least do not know how to do it). And the owner key can't do this.
But the important thing is that if we lost them, we loose access to change passwords, and if any of these 2 (owner or master key) are stolen, anyone can gain full control of our accounts.
Hope this makes sense to you.
Regards, @gold84