I was hesitant to pull the trigger on this upgrade for a long time. But wow, it sounds awesome. You can really tell it's BREATHING in the mid to upper RPMs now. The sound reminds me of my dad's boat when he'd open the throttle up, it's night and day.
I wish I could speak to the power gains by numbers. It feels more powerful, though I might just be twisting the throttle a bit more since it sounds so good lol.
By feeling alone, the cost is worth it just because it feels more satisfying to ride. If it's actually a faster bike because of it, great.
Caution: don't overdo it on the filter oil, I definitely oversaturated the filter. Mine has leaked down all over the rear valve cover and headers. I've really baked on some filter oil and it's made quite a mess.