I have it. It works really good. You can get great results without it also but it does seem to give a really moist environment inside the kettle. I smoked a rack of ribs using like 50 some briquettes with it. I have never done real long cooks like a brisket with it. I always wanted to but its just to easy to throw on my ceramic grill and let it cook. Someday I will smoke a brisket using it.
I've had good results with mine also. I've done ribs a few times, and one turkey breast that turned out amazingly tender and moist for turkey. I don't use it as often as I used to, or maybe as often as I should, but I still love having it around, it's simple to use, and can hold ALOT of meat when using the extra rack.