Hi Mike,
I bought a Rockwood that comes with the Reese Sidewinder from the factory. I towed the 5er about 500 miles with a slider and the Sidewinder locked out last year and have towed aobut 600 miles so far this year with the Sindwinder activated and the slider in tow mode and have felt no change on the road. It is very nice when parking or turning in tight spots. I don't have to get out and use the slider, I don't lose half my bed space with an automatic slider.
So far I am very happy with the Sidewinder.