Harley would like you to use everything Harley, they have a vested interest.
Ok,
When I had my 05 RK, I used Redline in all three holes. 30000 miles later no problems. Using synthetic in the engine did create a little more top end noise. The shock proof in the tranny proved to be a big plus, shifting was smoother and neutral was easier to find. Then there is the added cost of synthetic.
Today,
I had my 1k service on my Ultra. I am still not sold about the synthetic in the engine and decided to go a different route this time. I put regular dino in the engine, Redline in the tranny and formula + for the primary. Once again, a noticeable difference in the shifting. We will see how this works out for me.
Good luck!