Wow, does that ever bring back memories! Scroll back 50 years - "Instant-On" really was a marketing term for series-string vacuum tube radio and TV sets. A silicon diode across the on/off switch in reverse to the main B+ rectifier would keep the tube heaters at half-power by rectifying the AC so only half-cycles could get through. But this kept the tubes hot enough to start immediately when the diode was shunted by the switch, even though it did take a few more seconds to reach optimum performance. It worked, but was a terrible waste of power.
Back then the marketeers were tripping all over each other in efforts to come up with ever-more creative claims for the audio output wattage of hifi/stereo audio amplifiers. Can anyone top "Peak-to-Peak Music Power!"? The USA FTC (Federal Trade Commission) put a stop to that nonsense in 1974.