Right, I've had the Mel-8704R for about three months now - picked it up in February for £189 from a supplier down in Bristol - and I think that's long enough to give a proper verdict rather than the usual unboxing excitement talking. Short version: it's decent, but it's not the game-changer the American YouTube lot make it out to be.
I've taken it out to six locations since buying it: twice at a converted mill up near Halifax, once at a private residence in Shropshire (clients wanted the full treatment), the ruins of a chapel outside Dolgellau in Wales, and most recently two sessions at a supposedly active Victorian terrace in Sunderland. In genuinely cold environments the ambient temperature probe is excellent - very responsive, flags drops of half a degree or more reliably. The EMF side is... fine. It picks up the usual interference from dodgy wiring in old buildings, which honestly tells you more about the state of British electrical infrastructure than anything else.
My main gripe is the build quality for the price. The battery compartment cover is already a bit loose, and one of the lads on our team managed to crack the casing slightly just from setting it down on a stone floor. Not exactly rough handling. For nearly two hundred quid I'd expect something that could survive a night on the Yorkshire moors without looking sorry for itself.
Happy to answer questions if anyone's considering one. I'd also be curious whether anyone's compared it directly to the newer TriField TF2 - I've been tempted to grab one of those as a backup unit.