I've had one for several years.
I think it's a cool tool, but I think is best used in higher temp cooks.
In a low and slow cook, it holds temps down by shutting the exhaust. Doing this creates more creosote and will put a bitter taste on your food.
If you use less fuel, you can avoid this... But that kind of defeats the purpose.
At higher temps, like 350, it does just fine.