The OEM one is a hollow CF piece. Weighs almost nothing. The ebay ones are a solid piece, weighs more, but its minimal. Whether it has any real CF at all is a mystery. Also, the OEM one sticks up a little higher. Ebay one is more flat. I'd say in-between the factory lip spoiler and the OEM performance one. I've seen both, and both look good. In terms of durability, the previous owner had it on for a little over a year and it looks brand new still. If you're on a budget, I don't see a problem with the Ebay one. If you can afford it, go OEM like Tech said.
EDIT: The person also attached it using the supplied 3M tape. I know Betalink is recommended, but it might be overkill. Remember reading somewhere that somebody tried to steal the spoiler off of an M3 and it was put on by Betalink. The crook damaged the trunk because the Betalink was so damn strong.
EDIT 2: Just noticed you were looking at a Ebay painted one. Obviously no CF at all lol