
Because this circuit is based on linear regulators, the efficiency can be calculated as followed: +5 Volt regulator efficiency equals: (14 volts 5 volts)*6 Amps (assumed current draw)=54 watts given off as heat. 5 volts*6 amps=30 watts used by the system. efficiency= power consumed by the system devided by the total power acutally used or 30/84=.35 or 35 percent. Not very good. 
Using the same equation for the +12 volts yields the following: +12 Volt regulator efficiency equals: (24 volts 12 volts)*.6 Amps (assumed current draw)=7.2 watts given off as heat. 12 volts*.6 amps=7.2 watts used by the system. efficiency= power consumed by the system devided by the total power acutally used or 14.4/7.2=.5 or 50 percent. Better, but still not good. I would estimate the total supply efficiency at 38 percent. 
Compare that with a typical inverter that gives 60 percent or better, or a Switcher like the Sproggy that gets in the 80/90 percent range, and this circuit becomes less then desirable. The only reason to build it all would be the availability of the parts, or the inablility to obtain the speciallized regulators and inductors required by a switch mode supply. 
This circuit suffers from the same noise problems that most inverters cause. The noise can be reduced to an acceptable level by grounding everything including your amplifiers preamps etc. at the same point. I was not able to eliminate all of the noise from my system however. At one point I wound a Smaller transformer, it was rated at 1.2 amps I believe, and the noise got significantly worse. I quickly put the 4 amp transformer back into the system. 