Yes, fair comments. I think in some quarters there’s a tendency to just mention the 1% total without any qualification, so the end user is perhaps thinking they’re getting that on each of their channels.
With “derived” 3 phase monitoring, I think even the larger loads can be significantly out. Most loads here are single phase regardless of whether the house is single phase or three phase, and in a three phase house it’s common for the sparkie to distribute the larger loads across different phases. Add to that the observation that it’s common to see 10% variation in phase voltages and it becomes a big fuzzy soup of measurements. Tweak enough knobs often enough and you might happen across a combo that results in a < 1% error in the grand total, but I’d have little confidence in the per-circuit measurements (large or small).
It also varies a lot from distribution transformer to distribution transformer, so one intall’s ability to achieve 1% on the total is no indication that another one in a different location will, or even that the original one will continue to when some change is made in a neighbouring property (like installing PV).
Energex recently installed monitoring on the LV side of my local distro transformer (which I think services about 20-30 houses). They monitor both voltage and current on each phase. They’re due to sweep through and replace all the ageing 80A service fuses on top of the telegraph poles and I heard while they’re at it, they’ll potentially moves houses onto different phases to keep things better balanced based on their acquired data … they know which houses have PV, how big their inverters are and which phase they’re currently on.