Don't mean to resurrect an old thread, but was pointed here by someone.
As background, been racing track for almost 30 years, the last 20 or so as a Cat. 1. Those EAI Gold cogs are the business, with caveats: If you stick them in an everyday drivetrain (SRAM single-speed chain/FSA chainring), you aren't going to feel much. But as part of a full driveline (Sugino Zen Racing rings/Izumi Super V or equivalent chain), the difference is there. The best way to describe it is it feels like extra chain lube has been applied. Super slick. And the driveline is quiet, which is weird getting used to. As any track racer will tell you, noise means things aren't meshing the way that they should. I raced mine the entirety of last season, two track nights a week from June-September, and it looks like new. Magic? Nope. A difference? Definitely. The difference between winning and losing? Nope.
Whether someone should be spending $100 on a single cog is one question. Whether it is effective is another. Thanks for reading, and hope this helps the next time the question comes up.