On cars with totally flat back windows that the factory installed them on (like Mustang Boss 302's) - totally cool.
On cars with curvy, or worse, wrap around rear windows - Yuck! Every seen the louvers on a 2nd Gen Firebird? Tacky.
So for an FGF? I just say no for louvers!
Front spoiler? Cool! Rear Camaro-type spoiler, yuck! Trans-am type rear spoiler, oh yes.
Same thoughts on my 2006 Mustang. Factory rear spoiler that looks just like a '70 Boss 302 spoiler - gotta have it. Ugly flat 2007-2008 rear spoiler that looks like a tray the Sonic girl would put your burgers on, heck no.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI