the frequency responses are very similar. The Difference between them is their polar pattern (the direction from which it is able to capture sound from)

A SM57 has a Cardioid polar pattern which would look like a sphere coming from the capsule.

The Beta mics are a hyper cardioid polar pattern, which means the 'sphere' from the capsule is smaller round the sides and bottom (like a torch beam) if that makes sense,! :S this allows for whoevers using the microphone to get a more isolated signal (less spill etc.)