You can either run a reverse servo OR a matchbox.....or if you have enough channels, like on the 12X, you can run flaps on separate channels, and reverse it in the TX, and forget about the matchbox and reversed servo.

In my 4 y/o KC/Wren 160, with a 12X and 1221, I run no matchboxes or reverse servo. I also run 8411's all around. Haven't touced them since I installed them...... 500+ flights.

Take care setting up the flaps with 8411's. They will draw mucho juice if you stall them. Use an inline ammeter for safety.