IMO, ERA has the best shaped rear fenders of any car made, whether glass or aluminum. Unique and SPFs are a totally different shape than ERA. And while it is true that most people order the "street" rear fenders, they do offer "competition" flares as an option.
Here's another image courtesy of ERA's website comparing the rear fenders of various cars
edit-
I can't get the pics to display here, but the pictures can be found at
http://www.erareplicas.com/427/blue.htm
http://www.erareplicas.com/427/profiles/index.htm