So having received all the units I ordered, here's the results for the ratio of fake to real and whether they all differ much internally.
I had one other I forgot to include here, which came from DealExtreme and was a fake with the same red packaging.
So the results were basically 70% fakes and 30% real.
There's a good chance that the only reason I got some real ones was because I looked carefully through all the ebay listings for ones that had product pictures that were clearly different from the generic manufacturer images, and actually hinted at the units being real through the presence of the lamp and mesh at the end.