I suppose I'll weigh in. I've had my HKS Hi-Power Spec-L for about a year now.
It's in conjunction with a catless UEL header, the rest of the piping is OEM.
Also running an OFT off the shelf tune.
Installation was super easy and quick. Took maybe 30 minutes with the help of a friend.
Cold Start is pretty quiet, but I think some of that is that OFT runs run a much lower RPM cold start.
Regular driving, it's pretty quiet. Don't hear it much in cabin with the windows up.
High RPM's, has a great sound and decent growl, still not very loud.
Drone? I get zero, and I mean zero, drone. Cruising on the highway is quiet and pleasant.
See video below for how it sounds full tilt while autocrossing. External mic mounted at the rear license plate frame.