A Genturi may provide some added protection for those inside the TT it's being used on; however, it provides very little protection for those neighbors downwind from the Genturi's exhaust. I make this observation based on personal experience. The Genturi has zero control of CO once it leaves the top exhaust stack. At that point it's up to mother nature. Do you trust her?
Again, each person has to put CO risk into some kind of perspective that works for them. There are risks and there are opinions, but there are no guarantees.