IMHO this is an original: congratulations, it looks like the eBay one and £500 is a good price in my opinion. We talked about this Mae West a lot, as it is odd that the dope yellow paint was 'painted' on, not sprayed. But judging by the pics it looks original; the cotton is faded and one can see that it was pea-green originally. The bladder looks good as well, nice early date. It's rare also to have the leg-tapes added, but this was done by some pilots and the Air Ministry released information (if I'm not mistaken) on how to do this. Compared to any repro that exists, this is a lot different so I think it is an original. I know that someone can repro items to this extent, but then you would own a rare 'one off' so money, in my opinion, wouldn't be wasted.
I'm only a teenager so I am quite young, but I'd like to see if any of the old sweats can add anything extra to what I've written-they probably can!
Also Harry thanks for taking the time to take these photos, they really are excellent-worth adding to any visual collection for reference purposes.