The only thing I worry about in that scenario is that Tideace (these names kill me!), is using the BXT molds outside of BXT's process and QA. (That said, I'm not familiar with BXT, so can't speak to their reliability either.)I was poking around on ebay, and didn't see BXT seatposts for cheap like they used to be, but Tideace had one that looked the same for $23, so I ordered one. About 2 weeks later it showed up, and it looks identical to the BXTs I have on both my kid's bikes (which have been great). I suspect that BXT and Tideace might be related... Anyway, this one in 27.2 is 191g on my scale.
I guess my point is that eBay carbon is pretty risky. Seatposts and saddles probably not too bad, but bars and stems would freak me out.