A trial lesson is no different to any other lesson however; it is probably the first lesson, and may well be the last lesson, unless you do something to encourage the participant to come back for another go.
All aircraft should be operated in accordance with a Check List however; the choice of memorising it, or reading it, is one of personal preference. Personally, on a trial flight I will deliberately read it to inspire the concept of formality.
If this was a Private Flight, a safety brief is mandatory in accorcdance with Article 88. In a aerial work flight involving a flying lesson, the student is not legally a passenger however; before commencing Exercise 3 Air Experience, you should also have covered Exercises 1 and 2 which include the relevant safety information. You have a duty of care to ensure they know how to get out of the aircraft in an emergency.
What possible reason could there be to let the student use the radio on such an early flight unless they had a specific reason for wanting to do so.