Tests on a car, the same car, is as believable as it gets.

Best flowing muffler would be something crazy like a 5" race bullet. Does not mean that muffler is right for most applications, or would even make it a car run any better if it's just the wrong one to pick. People take the whole flow bench stuff too seriously. It's just a tool to measure change or differences between things, but it can't tell you what it will do on a specific engine, at a specific altitude, at a specific rpm range, ect. It's all about a combination of parts working together that you have to look at.

I can say the Aerochambers are good because my brother has them on a low 11 second car and it runs very close to the same with them off. So much so that it's not worth the effort to remove them. They are a baffled muffler that won't score high on a flow bench, but on a running car they do what they say they do.