Specifically, I was refering to the Mk.I's and II's. They did a good job against the Emil series 109's they encountered during the BoB, but at that early stage of development they were still somewhat crude. Fabric covered control surfaces in the case of the Mk.I, which tended to balloon at high speeds (such as in a dive), manual landing gear, float carburettors, only .303 machine guns for armament (except for a few Mk.Ib's with 20mm cannons).
I'm a huge fan of the Spit, but IMO it didn't really start to become effective until the Mk.V. Then, she truly began to take off! 8)