So maybe it's not that much more efficient but 6 tenths of an amp is nothing to snub your nose at. The 400 watt inverter ran the TV using only 5.2 amps or 5.2 ampere hours for every 60 minutes of run time. It was a mere 25% inefficient when compared to direct DC. Again this is a far cry from the 10% claimed by most manufacturers, and often incorrectly believed by boaters.
This certainly was not a very scientific experiment but rather a real world experiment designed to show what one item, a TV, designed to run on both 120 volts AC and 12 volts DC, will do run both ways.
It is quite clear that if you have the option to buy a device that will run on 12 volts DC vs. 120 volts AC, you should buy it. Inverting power from 12 volts DC to 120 volts AC, then back to DC again is a terribly inefficient way to power devices off your boats house bank of batteries..