The Z/28 is the first car to unlock in mastery requiring 300 licenses to unlock, but the car really isn't worth it. It's got painstakingly slow acceleration (worse than a Prius), extremely low top speed, bad handling, and horrible nitro efficiency. Considering it costs you 1,687,400 credits to both MAX and PRO, it really is just a credit waster. You should get the blueprints for the Porsche 959 if you want a good car.