The CurrentCost one
I have the TTL to USB convertor plugged into a HP Microserver and a Perl script that logs the instananeous min/max and calculates the average power level over 5 minute intervals. Bit of PHP and GNUPlot produces a web page for any given day.
The 5 min plots can spot things like SHMBO'd forgetting to switch the iron off or energy wasting gadgets like the "keep warm" kettle or filter coffee maker stewing the coffee...
A Pi Zero is perfectly capable of the data logging and web page stuff using the XML. Would need to convert the TTL from a CurrentCost to
3.3 V Pi GPIO levels. It would be trickier to to interface directly with a suitable current transformer as Pi's don't have ADC's. Aurdino's do, so a bit of signal conditioning from the CT and away you go.