You don't need the radio telemetry kit if you are happy with only seeing the telemetry data on the received video stream and control is only via r/c control.
If you want to show your position in real-time on a GCS map, or use the copter automonously and change the mission plans whilst you are flying for example, you will need radio telemetry.
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If you want to show your position in real-time on a GCS map, or use the copter automonously and change the mission plans whilst you are flying for example, you will need radio telemetry.