There are 6-7 types of Hallertau. Most Hallertau from Germany will be Gold or Tradition. Gold has the highest AA, 7-10%, T. 5-8%. Some Mittelfrueh is still around, and that can run as low as 1%, but it generally 3-4%. As far as I can find there is no Mittelfrueh grown in the US.
There's also New Zealand Hallertauer, which although it is a Hallertauer cross, isn't remotely like the other hops in this family.
So, the short answer is not much difference.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
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