The "Home Energy Monitor" you pictured costs US$240. So to be 'good enough' it must save you over $240 in electricity charges. How accurate does it need to be to do that?
Very low power factor with high harmonic content mostly occurs in devices that rectify the mains and are running at low power (eg. TV on standby) as they only draw current during peaks of the AC voltage wave. These devices contribute so little to your total power usage that measurement accuracy isn't particularly important.
high frequency electromagnetic fields are going to saturate the
ferrite in the clamp compromising the accuracy of the measurement.
No, saturation is only caused by excessive peak current. High current devices generally have relatively high power factors and/or sinusoidal current draw, so this shouldn't be a problem. At very high frequencies the Ferrite will suffer eddy current loss, but such frequencies should have very little energy. Also the coil will have a resonant frequency due to inter-wire capacitance, but again this should be at a very high frequency and so have minimal effect on accuracy.
To measure true power the energy monitor must multiply instantaneous current by instantaneous voltage, then average the results over at least one cycle. It may do this by digitizing the voltage and current at a high sampling rate, then calculating the result in software. Current (and voltage!) measurement accuracy will be reduced as harmonics approach the Nyquist frequency (half the sampling rate), and by the bandwidth of the conditioning amplifier and input filter.
In the end the only thing that matters is the reading on your power company's meter. If your Home Energy Monitor helps you to reduce that figure then it is doing the job, even if it doesn't read low power factors very accurately. TED monitors are purportedly calibrated to 2% accuracy. How well they can maintain that accuracy with low power factor non-sinusoidal waveforms is not specified, but it probably isn't important.
