Over the last few days I've been conversing with Current Cost, a UK based company which produces energy monitoring devices.
After I made a bit of a cock up (I eventually wanted a data cable after some testing with the unit in order to graph our rough power consumption and the Trec unit does not have a serial output) with the order they promptly handled and corrected my mistake.
When my unit arrived there was unfortunately the wrong sort of clamp, within the day a replacement was on its way with a little extra (USB-to-Serial data cable) to say sorry. The next day the clamp arrived and my Current Cost Envi is monitoring our apparent power consumption.
During the whole process the Current Cost staff were courteous and basically pretty damn awesome, and I'd highly recommend doing business with them to any one.
I've not yet decided how I want to grab output from the Envi yet: Perhaps an Arduino, perhaps a slightly modified WRT54G, however given that there's serial out, the fact that the units use Zigbee, and there's a fair bit of documentation out there, it's going to get done one way or another.