I got this answer from Eagletree when I asked about use with big gas engines:

The Guardian should be compatible with large gas engine aircraft and is able to reject most levels of vibration. However, very strong vibrations can impact stability. To check for this issue after mounting the sensor, perform a vibration test by securing your model to a test bench or stand and ramping up the throttle slowly while watching the AHI. If the AHI begins to pitch or roll significantly during this test, remount your Guardian sensor further away from the motor, wires and any other sources of vibration or electromagnetic interference.

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AHI means artificial horizon indicator. You need the Guardian hooked up to a computer thru the USB port to look at that.
I tested mine using an orbiter sander as the vibration driver. It drove the Guardian nuts. You definitely need to test it before you fly it.