I'm not sure I have anything to add other than what has already been said, but will give my 2 cents anyways.
I have the SNS with the open bottom. I resisted getting it for a long time because of the price tag. I used all kinds of different ways to smoke with my kettle, including fire bricks, water pans, etc... Each method worked.
With the SNS, it just does what other people are already doing with fire bricks and other charcoal management and makes it easier. It is a luxury item but it works. I have found it is easier to maintain constant temps over a longer period of time with the SNS than all other methods except for maybe the snake method.
Would I buy it again? Absolutely. Is it necessary? Absolutely not.