I don't have the GT/CS, I have a GT500 style (since I have a 14 mustang), the quality is nice. I haven't installed it yet, but their splitters bolt onto the car using the OEM holes. One thing to note, Cervini's splitters in an unpainted state are a white/yellowish color, so you'll need to get it painted.
2011 V6 Mustang - Premium 202A Spec (Pony Package) - SOLD!
2014 V8 Mustang - Premium 400A Spec
6 Speed Manual, 3.31 Rear
Black, Charcoal Black
Comfort Package, Security System