As far as RDL goes, I remember a few years ago when he was asking me about manifolds when I was getting ready to have custom ones made for my truck. We had lots of long conversations on the subject for a long time. I said a log style will be the right design for a turbo diesel application. It will last longer with no significant performance difference over individual tube styles.
He decided to go with shorty headers against my advice, but IIRC, he did use the sizes I recommended.
So if those are RDL's tooling and design, I guess he came up with an good idea. Might have got some inspiration at this site even.
At least with PPE, I will actually be able to purchase them and test them, 3 years later, and I will report what I find. To be honest, I was never able to purchase RDL stuff. I think he was worried I would "copy" them. RIIIGGGHTTT...