I’ve had a positive experience with the Cadence Optimizer.
You don’t need a smart trainer. Just a power meter and cadence sensor.
If you have a Garmin device you can add this data field:
Otherwise the Cadence Optimizer gauge is shown on the Activity screen of the Xert app on an Android smartphone. I am not sure if it’s been added to the latest iOS app or not.
The Cadence Optimizer is calculating your optimum cadence range based on torque so lower cadences at lower watts and highest spin at your top watts.
You can always perform cadence drills independent of the optimizer, but I don’t recommend going lower than the recommended range.
Also see: Workout Cadence Question