I wouldn't want a V10 without it. On the 305 HP motors, I feel the gains are understated (they post the same gains for the small-port 265 hp original V10s).
So much so, that when I finally broke the welds on my headers after ~300,000 miles and a broken motor mount (I thing the engine flopping around is what actually did them in), that I went ahead an put another set on at 430,000 miles.
It sure is nice being able to to pass other rigs, and sometime cars, while moving 22,000 pounds up a 6% grade at 60+ MPH.
Plus, the stock manifolds break bolts eventually anyways. Might as well mitigate that my adding more power;)
