I have a Rane MIC1 that comes with my RA27 analyzer. Rane specs are better then either the Behringer or Superlux, even though the Rane also uses a 1/4" capsule.

Research indicates almost all these measurement mics are based on the Panasonic 1/2" omni capsule, even the pricey Earthworks models. I guess the difference is the circuit used to drive the capsule, and quality control during selection.

I was thinking about using one of my Studio Projects C4 1/2" omni condensors for measurement, but its spec sheet only goes down to 40 Hz. My Rane is probably the real solution, but I have to build a +2 power supply for it, as its power requirements are unique.