Anyone used it with the AX100? Impressions? Can it replace a proper balanced shotgun for semi-pro usage?

Nope........that is basically just a mic element pointed forward. I would assume that you would get less behind the camera sound pickup from it vs the AX100's top facing elements, but do not expect even the performance of a short stock camera shotgun with XLR. I can tell you, with my X70's built in microphone grid, I can hear myself breathing very loudly.....it's horribly annoying, as I am breathing through my noise.

Paul