Howdy BurnerLief:
I believe that the port divider alone will help to improve and balance flow from cylinder to cylinder. It, by itself, may not be noticeable to the seat-of-the-pants dyno, but if you believe that every little bit helps, then it is worth it. I used one on a much modified head with a modified cast exhaust manifold and 2" exhaust on my 250 for awhile before I bite the bullit and invested in a header.
The point of the divider is to seperate each exhaust pulse for as long as possible and to even flow. How much? Maybe 2 to 5 hp depending on rpm range. The divider, along with a performance exhaust system, maybe 5 -10 hp, again, depending on the rpm range. Add a performance cam and improve intake and it becomes increasingly important.
If you are planning to add a three angle performance valve job and increase CR along with the divider while the hed is off, you will notice the difference. And you will be ready for headers when and if....
Adios, David