I doubt it will increase horsepower by itself. Now if you had a boost leak because your noisemaker wasn't sealing right then you could see some power out of it. I have the full hot pipes and they are very well made so if you want to eliminate the noisemaker and a potential boost leak this is a great alternative.
Nice Price indeed. FWIW purchased mine many years ago unpainted,naked for $200.00 and recently gave it away to a lucky member for Free.
I later ordered a set of Gloss Black Hotpipes which is on my current setup and IMHO couldn't be happier. Z