I've got a Playskool one that's never been fitted, and if I'm honest, I'm probably never going to. Would let it go for what I paid; £50, includes a "fitting kit", (pair of bonnet pins).
I'll be honest, I bought it with the intention of building up a pair of patterns on it that I could pull a mould off so that I could make some separate covers for the lower suspension wishbones. Instead of just having them sticking through the diffuser.
Got as far as half a dozen coats of wax on, ready to start building up the profile I wanted, when Julian announced his new diffuser on Facebook, with suspension pockets built in. Doh! Didn't seem much point after that, then I started on the Honda project, and it just got filed in the shed with the other spare parts.
If I ever change my mind and fit one, it will probably be the Aerodynamix one!
(How's that for an honest ad!)