Tuned properly fuel economy is as good as stock and sometimes better. Power is absolutely better at least it was for me. I could roll on sixth gear and I can't do that stock. I used SERT only to maintain warranty and not because I think it is better.

 

I run it and made the below numbers on my 98" BBC. Best mileage was 49 mph while riding the Blue Ridge Parkway. Great product.

 

I have it on my 06 RK. After some self-induced issues, I really like it. Other than Stage1 my bike is basically stock but I think it seems to run better. Now that I've got my "issues" ironed out, I'm going to start tuning for a little better mileage.
The issues had to do with exhaust leaks that screwed up the self-tuning loop, by the way.

 

Not to sound like a broken record but, I've got it and I think it's great.
I installed it myself. Installed the map for D&D Fat Cats and Ness Big Sucker. It fired up the first time I touched the starter button and ran like a top since.

THEN, while at Bike Week in Daytona I stopped by their booth and talked to a tech guy there. He invited me to bring the bike in to the controlled area where he hooked up from his laptop, made some adjustments, and got me out of there within 20 minutes. I was happy before but the bike runs even better now.

I'm going to buy a Dyna sometime this month for my kid's 18th birthday. Thundermax AT will be the very first mod! You could say I recommend it.