I have gloss black side skirts from
C7 Carbon (similar to those at the link you provided, with a bit less "chunky" outer edges), and they have great quality & fitment at a not so great, but somewhat acceptable price.
Two things you may want to consider, though:
- one, neither aftermarket side skirts nor the OEM ZL1 skirts are compatible with the GM splash guards, there is an overlap in the front that you'll have to be somewhat creative in resolving if you insist on these splash guards (I recommend ZL1 Addons or even better,
Rokblokz if you don't mind the mudflap style); and
- two, aftermarket side skirts are all hollow bottom to allow post-assembly installation, unlike the real ZL1 side skirts that are integrated with the rocker panels or the GM ground effects package skirts that both have a flat bottom, which also means rocks from underneath will hit and may damage the rear end cap of the skirts.
At some point there were ebay sellers that offered ZL1 takeoff rocker panels with the integrated side skirts and already painted, you might want to check those out as well if you can't live with these limitations, but even then the GM splash guards will not fit ZL1 at all, I'd probably just choose a different product.