Now that I've gotten to use the Slow N Sear more I think I can give it an honest review. I've used it about 10 times or so with my Weber Kettle 22inch. First off I have to apologize for my comments in the past about the Slow N Sear. I complained about the temperatures not holding properly and totally gave off the impression that there was some serious false advertisement when it came to the unit.
The Slow N Sear does extend the life of your charcoal by quite a bit. There's no comparison really. I tried doing the two zone method with the slow n sear and a different time using the same amount that would fill a slow n sear piled up on the side of the kettle. The Slow N Sear gave me a lot more hours and also made it easier to hold the temperature.
My main issue with using the Slow N Sear is I tried to get my grill hot too fast. If my goal was 250 I'd try to get it there as fast as possible. This made maintaining that temperature very difficult and it's tough to hold a temp using any method. I found if I let the temps creep up which is what is recommended by the slow n sear instructions it worked as advertised. I was even able to walk away from the grill for hours without fear of some crazy temp swings.
I cooked 1 butt, 2 shoulders, 1 whole chicken, 2 racks of ribs, steak, burgers, chicken breasts and various other things. All of the food came out great. The Slow N Sear just makes things easier. It's definitely worth the price and I recommend it to anyone who's been looking at it and not pulling the trigger. Make sure to follow the instructions carefully. Any straying can lead to improper results with how your kettle cooks.