The Personal Trade Copier duplicates orders between two instances of MetaTrader 4 running on the same computer. The communication is almost instant. Lot sizing can be adjusted between the two accounts, and you can limit the copying to particular symbols or magic numbers.
The Internet Trade Mirror duplicates orders over the internet between copies of MetaTrader 4 on different computers. Senders can control which trades are broadcast. Receivers can control which trades are copied, and can change the lot sizing and risk settings.