Acknowledged. I have a couple of multimeters in the truck. I leave my oscilloscope at home.
I use the "nightlight" to test GFCI's and it is GOOD for that. It detects anomalys in wiring to some degree, enough to tell my client, "this outlet or this circuit needs repair."
The voltage sniffer tells me if voltage is present, such as in K&T.
We do a visual inspection, and a quick check for obvious problems. I don't want to portray myself as a wiring expert, just a generalist. My clients may know I'm using a cheap tool, but I try to produce a knowledgable conclusion, and they're ok with that.