I just had the Nameless EL header installed on my car a couple weeks ago and was very pleased with the results. I have a Perrin panel filter, Nameless header, and Perrin cat-back. I'm still using the OEM overpipe and frontpipe.
I created my own "hybrid" tune in RomRaider by researching different OTS tunes, taking advice and guidance from a local tuner, and spending lots of time collecting data logs and slowly experimenting with different aspects of the tune. I then paid for a few a dyno pulls to see how my setup compared to a stock BRZ in the shop's dyno database and here are the results:
Overall, I can't complain. I know a pro-tuner could get more out, but I'll worry about that when I upgrade from the stock overpipe and frontpipe. Mating the 3" header to the 2.25" overpipe was comical but there's no leaks and the gains are still decent. The only downside to this plot is that the stock baseline was not my car and run on a completely different day.
Hope this helps!