I know nothing about the preamp, but if the C1 is anything like the B1, it's GREAT!!! The B1 is clean, flat and really sounds nice when you close-talk the unit.
I'm just testing the C1 and you do have to close talk it as well...and it sounds OK... Although cannot say whether its any better than the electret insert I mostly use for appox $1-
Its a nice looking Microphone though but its like in 2 halves each side is out of phase to the other....