are geese as good guards as I've been led to believe? And do they perform as deterrents or alarms or other?
No! Our ganders will go for people when their geese are sitting, but otherwise they are fairly gentle souls. They do make a lot of noise sometimes, but as we have never had intruders we don't know if they would make a different racket for them. They sleep inside so would only be on patrol in daylight hours.
We rely on the dogs and whopping big padlocks and the like. Anyway, we don't have much to steal - it's all second or fifth hand.