For fun, I repeated their test using the BM869s that I used for life cycle testing. This meter has the later firmware which I expect would be closer to the OPs). I also used one of my Fluke 189. Both meters on the bench, sitting on a grounded ESD mat. I tried with and without leads. Leads were 27" long. I left them untwisted laying across the mat. I used that Caddock USVD2 2ppm 20.0007Meg resistor that is mounted in the foam as my reference. This part has the banana connectors and will plug directly into meters that use the standard spacing. Meter were set to record their min/max. I then waved my hands around the meters and also got up from the chair a few times (maybe 2 feet away from the meters). Keep in mind that we are in the middle of winter and the house is dry which it great for ESD.
With the leads:
Fluke 189 Max: 23.256M, Min: 7.772M
Brymen BM869s Max: 22.275M, Min: 17.800M
Without the leads (resistor plugged directly into the meters):
Fluke 189 Max: 20.032M, Min: 19.682M
Brymen BM869s Max: 20.134M, Min: 19.899M
Are both of these meters junk? Maybe but I rather like them. I suspect that the Fluke they show has a much higher voltage with their resistor attached than their Brymen. For the people wanting to look at LEDs with their $400 meters, the 87V may be a better choice.
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Added picture of the test resistor used. Also, I want to be VERY clear. The test I ran is not controlled and I am NOT suggesting that the Fluke 189 is more susceptible than my Brymen BM869s!
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Because I opened the question of the test voltage, using the same 20M resistor, I measured the voltage across it with my old electrometer. Obviously, at 20M we need the high input impedance. I tried my 87V that I purchased brand new a couple years ago specifically for testing. It's seen some abuse but I doubt it would have any effect on this measurement.
Fluke 87V: 3.590V
Brymen BM869s: 0.735V
UNI-T UT61E+: 0.814V
UNI-T UT181A: 0.809V
Of the four meters, it would make sense that the Fluke 87V would have better immunity in this particular case but again, this is not how I would use the meter and I'm not a fan of these high test voltages (for electronics work). But, if I needed to light some LEDs, this would be the ticket.