The Ebay link to the UK e-store is,
eBay Store - Smart-Green-Shop: Energy-saving
To monitor the AC wattage output of your inverter, the clip-on current probe
has to be placed over a
single leg of the AC line. Just clipping over the whole cable won't work.
Here's some info about a clip-on non-contact sensor.
Mains AC: non-invasive voltage and current | OpenEnergyMonitor