The U2 was on the verge of a stall when operating at near its service ceiling and approaching the speed of sound. The usable speed range under these conditions was only about 10MPH which made for very tricky piloting indeed. The turn spoilers may have been needed because of these unusual operating conditions.

Very high aspect ratio sailplanes (model or full scale) do not generally need or use turn spoilers. The high aspect ratio wing at slow speeds results in lots of adverse yaw which is overcome with aileron differential (more up than down travel) and rudder compensation for coordinated turns. That’s what works best at our altitudes and speeds.