I'd certainly agree with Brian's comments on air flow related to the Mk3 , the direction of flow with the fan works a treat when stationary or moving very slowly, taking the hot air up and out. At faster speeds, the fan doesn't run anyway and from what I've been told, the air flows the other way, down and out then.
I find it reassuring to have in there , especially when sat in traffic at 30C plus. I am convinced its a good thing to have and if I was having the swap done again, I'd definitely want one in there.