Socket tester for AC power outlets

[LCHIEN]

I have this $13 Socket tester from Amazon
It checks at a glance the proper grounding of your outlet (three LEDs at the top) and gives the Normal Voltage (Line-Neutral) and also indicates Neutral to Earth voltage imbalance (a few volts is OK)
It also tests the functionality of your GFCI, if you have one.
I leave it plugged into a socket in my shop, I can check the line voltage at a glance if anything seems off.
It has 3-prong AC plug in the back for plugging into a socket.

here's my actual unit doing its job:


when I turned on the Dust collector the N-E voltage increased to 1 volt.