The M300 is Gefell’s small-diaphragm FET condenser, aka 'pencil condenser.' It provides a fixed cardioid pattern and compact size for ease of placement.
Frequency response is flat from 100Hz to 2kHz, then exhibits a gentle rise to +3dB around 10kHz. -3dB points are at 40Hz and ~18 Hz.
The mic’s capsule, designated 'M3,' employs a 16mm Mylar diaphragm, coated with gold. The housing is ceramic rather than the more-typical metal; the advantage, derived from the company’s work on test and measurement mics, is that ceramics have less susceptibility to change due to temperature.