Can I use my own Microphone with Metronaut?

Yes!

Metronaut automatically chooses the last microphone you have connected to your device as long as it is a Wired Microphone.

You can verify or change the microphone in the Practice Screen, by choosing Volume thenExpert Settings and in Microphone Settings (see screenshot).

Note that by explicitly choosing a different microphone than the one automatically selected, it will be remembered and used in every session (if the microphone exists) on the same device.