There is no advantage in going to those approved mechanics if anything the pits might be better due to rushing. I had my sticker off at pebcos after second attempt. They failed me for my head lights being to dirty and the tint. The time before I went to pits and passed with ease they never even said anything about the tint. Pebcos spent over an hour on the car. The approved mechanics go over it more than pits.
The only advantage is the experience. The Pits suck for that.