I may get shot down but my understanding is the AGU is the earlier engine <-1999/2000 which is less tunable as smaller turbo but stronger engine internals.
AUM is more tunable due to a better turbo, but not such strong internals. Some people get the AGU engine and then add the later turbo for the best combo.
Depends on your plans, if you want to map the ECU go with the AUM, if happy with 150 odd BHP go with the AGU.