When evaluating bullet tweeters, prioritize the diaphragm material, typically Titanium or Aluminum, as these offer the high-frequency rigidity needed for crisp sound. Pay close attention to the voice coil diameter (common sizes are 1" to 2"); larger coils generally handle more power. Ensure the impedance (usually 4 or 8 ohms) matches your amplifier's output. Additionally, verify the frequency response range, looking for units that can reach 20kHz or higher with minimal distortion, and a sensitivity rating above 100dB for high-efficiency output.