In the mid/late 90s I was regularly flying as observer with RAF and other nationality military test pilots at Boscombe Down, and if I wasn't flying, I was often in telemetry with a headset on for testing single seat aircraft.
They all did a verbal take-off safety brief, even if flying solo in a single seat fast jet. I reasoned then, and have done ever since as a pilot, that if it was good enough for them, it was good enough for me.
The reasons should, I hope, be obvious enough to everybody here without my needing to repeat them.
G