128I performance side skirts upgrade question

[eva]

I am going to replace the side skirts by this performance side skirts.



After searching online, I found

Turner Motorsport has it for $409, a pair of un-painted side skirts only.
ECS Tuning has "AERO KIT SIDE 2 DR", everything (mounting parts) included, for $271.32.

Both of them claimed original BMW parts with same BMW parts number.

My question is
Is ECS Tuning trustable? (I never ordered BMW parts from them)
How can the price be big different?

Does anybody can answer my question asap?
Thanks.