FWIW - I have TTi's on the Demon. Performance is pretty good (better than most/all out of the box but not as good as a custom set). However, working on the car with them is a b!otch. So, I bought a set of new ProParts headers as the ease of working on the car is greatly improved. However, when I got the box, I instantly noticed the tube lengths were all over the map - uh oh. Then I tried to test fit them (B block, -1 heads, A Body) and a few of the tubes lined up directly to the center of the frame rails - so lots of mods were going to be needed.
I had already sold my TTis as I was confident in the recommendations - oops. Fortunately, there was another member on the board who had a new set of TTis that he was looking to get rid of and wanting to buy a set of Pro Parts - so it all worked out for both of us.
One other thing - A guy I used to race with had nearly the twin to my car - same body, gearing, trans, rearend, engine. His car was 300# lighter, but I was quicker and faster. The only OBVIOUS difference was I had TTIs and he had Pro Parts.
And I agree with what was said above - Mazzolini is a great guy.