The Gold Ring allows you to set the actual F/D on the side at a range it is capable of. I forget where I have mine set now, but it works pretty well.
I'm a newbie to FTA, but I have worked in RF for many years which hopefully means I'm not clueless. A few weeks back I scored an immaculate Pinnacle with a Corotor II/Golden Ring. I just finished setting it up and was lucky that the previous owner meticulously saved every bit of documentation related to the dish.
My Corotor is marked down to a f/D of 0.30 which is, as mentioned before, higher than the Pinnacle's specified 0.278. The Golden Ring instructions indicate it should be used for f/D ratios of 0.32 and below, and that the Corotor scalar rings should be set at 0.36 when it is attached. The Chapparral website explains the use of a Golden Ring is "a trade-off between gain and system noise" and that the Golden Ring only reduces terrestrial interference and does not increase system gain. The instructions say "an increase of 0.75 dB in carrier-to-noise ratio is possible on an accurate reflector", which is nothing to sneeze at but still not a lot. Realize that in the best case a 3m dish with a Golden Ring will perform like a 3.1m dish without.
While I briefly tried the Corotor (it worked fine), my receiver setup is such that it would have been impractical. Instead I picked up an ADL-RP3-2+2B, which is a dual orthofeed. It is specified down to a f/D of 0.3, that in my quick-and-dirty tests of the Corotor without the Golden Ring seemed close enough. I'm now running with it and can report that the dish will lock and view signals down to about 8 degrees above the horizon. Around that point the neighbor's steel fence kicks in. I am looking into modifying the ADL feed for a slightly lower f/D, but that will be a project down the road.