Its fairly good, but its giving up alot of potential areo if its a direct copy of the STi.
I can't see under it, but I'm doubting they integrated a front diffuser. The viper ACR and Mustang Boss 302 both use it to good effect. From what I've read this is as big of a deal as having the front splitter. Venting the wheel wells and hood area is also critical and the STi seems to have no venting of either.
hitting up the rear wing, if you don't have rules or your rules allow it, moving it rearward increases effective downforce at no cost to drag.
More interestingly
If I had some resources I'd play with the wings of this era as most series were deep into aero regulation and F1 is starting into the deep end of stuff you can only do with huge budgets. Here they were still allowed to put a rather huge wing outside the wheelbase and look at just how low it is. This according to everything I could find should produce quite large amounts of downforce without a huge drag penalty. The wing has lots of leverage on the rear tires, keeps the airflow off the top of the body clean, and should extend the low pressure zone increasing the effectiveness of the rear diffuser.
oh and please, please don't follow the idiotic trend of people putting rear wings at roof level or higher. The air may be clean but its alot heavier for less effect. There is a reason that racecars in the 60's abandoned the high wing in very very short period of time
Lots of structure, no areo benifits from the wing/body interaction.