The CRC is enabled by default to be compatible with the Arduino/RadioHead Library implementation.
To disable the CRC either:
1)disable it when instantiating the device (add crc=False) to the kwarg list
2)change the setting via the enable_crc property (eg. rfm9x.enable_crc=False)
This will have minimal impact on existing CircuitPython to CircuitPython communication because the CircuitPython library allows the "explicit" header setting to determine if the CRC is used. The radio uses an additional header to determine if the CRC is present. The RadioHead library has an extra check to verify that the transmitter and received have matching CRC state. In Circuit Python, even if one side has the CRC enabled and the other does not, the packets will be received. The internal header determines if the CRC is present. Existing deployments that do not have the CRC enabled will still work as before.
To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-rfm9x`.
Read the [docs](http://circuitpython.readthedocs.io/projects/rfm9x/en/latest/) for info on how to use it.