I guess I don't understand it. Website recommends you install that then get the $168 stack extension for more draw??? I think they want your $.
I think the idea is solid, if it slows down at the inlet you need speed it up at the exit.
If it spreads the heat out evenly, I'm a supporter.
Quick and dirty exhaust extensions are a real thing, not spending extra money is also a thing.
They tell you to buy a bigger hose .So you hook up your water hose to the faucet. Then you cut the inflow down 1/2 .
How you gonna speed up outflow at the other end ?