Measurement microphones generally don't make good testing mikes. They have omni directional characteristics, so most of the measurement is about the noise environment and room reflections rather than the test speaker.  In addition they are expensive, frequently need dedicated pre-amplifiers and power supplies, and are just not robust enough for the production environment.

The linearity and long term stability that make a measurement microphone a measurement microphone are not needed with comparative testing.  Changes in your microphone's sensitivity and linearity are accommodated by the periodic re-calibrations.

Any reasonable quality microphone with a cardioid characteristic and an acceptably extended high frequency response is suitable.  We supply and recommend the Audio Technica ATM33a.

Mikes with a hyper cardioid characteristic do give greater noise isolation but they tend to be less linear at high frequencies.  We have found cardioid mikes the best compromise.