The 121GW was certified by ETL as well. After seeing that meter pass their certification while not being able to perform a simple autorange, I have low confidence in their abilities.
With the UL 61010 not being an open norm (you have to pay dearly for it, and obviously I'm to cheap for that
), I don't really know what's in there, so I don't know if it's a matter of abilities or a matter of that the content and demands set out in the norm have any real competence or high set standards of quality in them. I also don't know if its standards concerning safety or robustness or whatever; I think its mostly (all?) safety stuff, so I imagine they want to see double isolation, isolation values of the casings and such. Maybe that's why a non/bad functioning meter can perfectly pass that norm.
All I know is that DMM reviewers usually point it out if the DMM has it or not when they review a DMM.
Browsing through the Intertek database I also saw that the popular Uni-T UT-61e is UL listed. Apparently that also meets UL 61010 standards. That immediately shows that the UL61010 standard at least isn't of much use for the gas grill repair man
And in the Uni-Trend listings you can then also see that Uni-T makes products for amongst others AMPROBE, EXTECH, GRAINGER, GREENLEE, KLEIN TOOLS, MILWAUKEE, TENMA, Southwire, VOLTCRAFT, and BOSCH. Always interesting to see that (but not really unheard of of course)
The inside input protection of the Amazon Commercial 90DM600 as reviewed by Kiss Analog certainly looks similar with it's arrangement of PTC's and MOV's to the CEM DT9939 you've tested so indeed maybe it performs similar on that aspect.