I bit the bullet and just ordered the original seat post from Ergon. Outrageously expensive but I am 50+ and cannot afford a fall or a broken stump of carbon fiber up my bum! Where I live the roads are made of roughly compressed chips (plus potholes, patches etc.) and I ride in normal clothes, so I really need it (had a Thudbuster with the old bike).
I inquired with the eBay sellers and their seat posts do not even come with the special carbon grease/paste which is required with carbon seat posts (which you can buy separately of course, but makes me think they're not really like the genuine ones).
Another reason is delivery time, I just got a mouse pad from China and it took exactly a month. The Ergon will be here in two days.
However, I am 80% sure the Chinese would probably be the same as Ergons so I feel ripped off already! I think you're right to go ahead with the Chinese.