We are the distributors of the "throttle" in question and have sold many thousands of the little marvels. The term "throttle" is used in its colloquial North American form as in "restrict" (in this case RPM) as opposed to its strict mechanical interpretation. Even Cox called their version of an RPM reducer a “throttle ring” although, technically, it is an exhaust restrictor.
We make no bones about the throttle being an airflow restrictor. However, it is incorrect that the throttle merely enriches the fuel / air mixture.
Because of the unique nature of the “Surestart” choke tube, the venturi effect that is created actually also reduces fuel flow; not exactly proportional to airflow but nonetheless at a ratio conducive to the engine functioning properly at lower RPMs.
It is not a requirement to purchase head adapters to successfully use the throttle, as the throttle permits engine operation at sub 7,000 RPMs with the stock head; low enough to land virtually all aircraft designed for use with a Cox .049 reed valve engine.
Head adapters can be used if a modeller desires an RPM increase beyond what a stock head would provide or a low idle beyond what a stock head would provide.
Our throttle has been reviewed by a major model magazine (Fly RC) here:
http://www.coxengines.ca/files/review.pdf
and, so far, no one else has successfully launched a competing, low-cost, alternative, except the ubiquitous throttle ring; which does not permit the simultaneous use of a silencer / muffler.
Bernie
www.coxintenational.ca