After all the time and money I've spent designing and building my own, I'm winding up with basically what the thermal is - a traditional resonator and a helmholtz chamber. Ultimately it will have cost me probably twice what the Thermal costs from Ron. I'm not regretting it, I have fun with it and it's easily my cheapest hobby project in a long time, but if I were going to go out and buy an exhaust "off the shelf" I'd simply buy the thermal. The fact that I did all the testing and math and wound up with a helmholtz chamber roughly the same as thermal's means they did substantial R&D and specifically targeted the same "drone range" that I did. I don't consider my spending a waste of money, I've spent more money on less fun, but again, for a "buy it and leave it alone" solution I think the Thermal is the best I've seen.
Yes, I'm gushing about the Thermal and I don't even have one.