I've owned a GPR.
Value for dollar I give it 7/10, I give my Yoshi 8/10.
Quality of workmanship, 6/10, I give my Yoshi 9/10
Hardware for install was a bit second rate in comparison to pipes I have owned in the past.
GPR was on the quiet side but that varied on which of the supplied noise suppression hardware you used.
Yoshi is either DB killer in or out, by the time it starts to sound really good, it's probably time to repack it.
Would I buy another GPR, probably not, would I buy another Yoshi, most likely.
This is the only picture I have of it, you can see the DB killer in the end of the pipe along with the outside diameter, there was also another DB killer you could fit on the entry to the muffler, or you could leave them both out.
This was on a Benelli Trek and making the pipe to free flowing just farked with the fueling, so I ran both DB killers, went well and had nice note.