Music that can be turned on or off and follow along with BPM matching the intensity of the interval. Also motivational voice telling you to “go” at the beginning of an interval or “almost there” toward the end. Things like that to help the workout mode be a little more exciting.
Please no to the voices! Not fussed on music as you can just put your own music on if you wish. Personally I hate music during workouts but if it could only be turned on (defult off) it would be harmless.