Once a couple thousand feet in the air, I commonly give passengers the controls. In busy airspace, it frees me up for navigation and ATC.
Doing intros in gliders, same deal.
And yes, I monitor very carefully.
Some selection is necessary. My nephew with cerebral palsy cannot control his movements and simply cannot be in any seat with access to the controls.
That said, our club commonly operates Freedom Flights for the disabled. They have to be lowered in with a hoist, but a number can fly the glider through aggressive maneuvers. That said, it's the senior instructors who fly them.
There is the type who takes a firm grip who needs to be admonished that a light touch is the way to go.
In gliders, you really do need a careful preflight briefing about keeping hands, legs and feet well clear during takeoff and landing when full control movement is often needed.
The regulatory environment varies with jurisdiction and with time; so what was once common practice may become proscribed.