Had them on a few cars. On some of the cars, I didn't even know they were there. The average modern 6+ speed automatic transmission shifts better than all but the best of the world's drivers, so I let it be. The transmission generally knows when it needs the torque and when it needs to shift. I leave it alone. I generally don't have diagnostic equipment hooked up to the car when driving (it's a car, not a test cell) thus determining the efficiency of shift points, engine braking etc. is all just speculation.
