When I was looking, I decided against their pins due to the feedback that they were scrappers. Granted only 4 in the last year, but how many people can spot dodgy pins and then go to the bother of leaving negative feedback? There are a lot of pins out there which either didn't hit quality control and should have been scrapped, or the factory's produced extra unauthorised pins (without usual attention to finish).
They've got a number of indivdual pins listed at the moment that I'd question, mostly due to:
Poor finish eg metal feathering round the edges not properly filed off - if they're being sold by Disney there's high quality control.
Having 5 of the same 'limited edition' pin listed for £2 (even the biggest editions are about 3000, you'd only really buy a number of the genuine ones to sell on for a profit, but that's way under cost price)
Incorrect character details (Dale's teeth but Chip's nose)
Only showing the backs of the pins in a handful of photos
At the end of the day, most Disney pins off Ebay are tradeable in the parks, but because people don't check, not because they're legit! You won't be able to swap them with a collector (or possibly clued-up staff), but they'll probably be tradeable with Joe Public (who have most likely also bought a job lot of cheap pins off ebay!).
And if you don't decide to go for these pins and buy direct from Disney (the only way to guarantee they're legit), make sure what you're swapping for looks alright. It would suck to swap a £6 proper pin for a 50p fake!