Unit seems to be good, with a few quirks. As others mentioned, color at night is pleasing, a little hard to read during the day. I went ahead and tested it with a power supply and a couple of meters, with a Samsung phone and a Samsung tablet connected to the device.

Comments:
At first I was surprised that my vehicles were reporting voltages as high as they were (old Toyota at 15.5V at 3000 RPM). With high voltages like this, the unit switches readings faster between amps and volts. Even a modern car was at 14.4V. Not out of spec but I expected more like 13.8.

Test results:
I started off at lower voltage to see what it would do. My test rig is pictured. Note that supply wires were not large, and I think I was getting some voltage drop even at lower current like 1A. Note that I did not measure output current, I only measured input volts and current, but the output cannot exceed the input V*A.

At low supply voltages like 10V, the unit would turn on, try to supply current, run out of supply, and turn off current. This raises voltage again, and it tries again. Not unexpected at all.
At 11.7V, these effects went away and the unit could supply a steady reported 2.73A (on the output side) to my 2 devices. Your car would be off and battery depleted at that point, so that is a good result.
Some mentioned varying voltage readings and it measured that way too. The USB devices (phone, etc) control their own charge rate. They seem to be attempting to draw a ton of amps, this lowers the output voltage (guess, not measured), and the load devices then reduce their demand to bring the output voltage back up. Once back up, the units attempt to draw more, and the cycle repeats, with less than perfect feedback controlling it to a non-steady state, which is why you see some cycling in volts and amps. This is probably normal but I would think the devices would learn an optimum draw rate and attempt to hold that.
The voltage was right on, whatever the display said was within 0.1V of true input voltage measured at the terminals, but it did vary by ± 0.3V or so as the cycling was happening. I think with larger wires on the input side I would have seen less of this.
With 2 units being charged and both screens on, the max input power was 13.3W (14VDC at 0.95A). The charger reported 3.63A on the output side at that setting. 3.63*5V = 18.1W, which is definitely not happening (output power cannot be more than input power). So either the amp reading is correct, but the output was drawn down to 3.7V as more time is spent with the gate wide open to the battery (most likely), or the output voltage is really 5V and the current is overstated. I didn't attempt to connect to the output side, so I don't know which is correct. The current readings were more reasonable (within 10% of input power assuming 5V output) at lower charge rates. I ran the unit for hours in my car and noticed that it was barely warm, so its power conversion is quite efficient.
USB charging can be pretty involved with few standards, so without more measurements, it's hard to say whether the current is correct, but it definitely followed the loads I was giving it.
The charger was not enough to keep up with my Galaxy Tab S, but almost. It will drop maybe 10% during a long trip in bright sun with bright screen, even with big cables. But this is no different than my Anker charger, which I consider to be excellent. So the unit supplies at least as much as the Anker which is rated at 4.8A total, and it is a beast, so I suspect the charge circuitry on the tablet is just not up to the task of keeping the battery at 100% in bright sun with the screen on 100%, no matter what charger is used (the Anker and the Jebsens have done the best I have seen). Adding a phone to the mix made no difference to that result, so it is not a power supply problem.

Overall, a good unit. Please comment if you measure and compare the output current.

This works well as a voltage meter, current (amp) meter (for usb charging), and a dual usb charger. The display is larger than most, and easier to read. The display alternates between voltage, and amps to the usb port (if something is charging). You can see the battery voltage by turning the car to the "on" position, but not starting it. Then you can see the alternator voltage after starting the car. It's a quick, easy way to monitor the most critical aspects of your car's electrical system.

The blue led display is a little hard to read in daylight. It's not dim, the problem is the surface is glossy, and reflections of the sky through the window, or things in the car obscure the numbers. You can shade it with your hand, but I don't recommend that while driving.

This comes with a sheet of instructions and specifications. However, you don't need the instructions. It's very obvious how to use it.

This sticks well in my lighter outlet. I have had no problems with it popping out. I'm sure that differs between car models. If you have trouble, I suggest tightening the fit by putting a little electrical tape (or any non flammable tape) on the plastic part of the shaft. Don't cover the metal contacts.

To clear up any confusion, this does NOT monitor the overall current (amps) pulled from your car's battery. For that, you would need something wired into the car's battery cables. This monitors the current (amps) output to connected usb devices.

Sister-in-law has problems with her car and is always worried the battery is going to die. plug this little sucker in and when she turns the key, she knows she has enough juice to start the old car. Great for piece of mind, and when she sees the Batt. is getting low (She doesn't drive far so it doesn't get charged like it should) she gives me a call BEFORE she has a problem and we put the charger on the car. Great little device. I'd give it 5 stars except... the display is inline with the plug which makes it harder to see. If they'd cock that display about 45% it would be much easier to see from the drivers seat. But it does work great.

When I found out it's an ATG's, I ordered one. But will get more to give to my employees for the coming Xmas.
Tested on my wife's F40, my ATG Gold Areo T-Rex Kim X and daughter's Civic.
The voltage readings are on par with my RMS meter and the two USB ports work well for charging.
You will noticed that number will be jumping around.
This is because the circuit lower the current rating so it will not kill your unit that is/are being charged.

And if you are new & wanting to ask does it do fast charging?
ATG says to stay away from fast charging chargers. Unless you like Apple products & love to make them rich.

A fast charger is only good if you need it in an emergency.
But the drawbacks are that it will kill your battery or can blow up your unit if left unattended for a long time.

Just like many today laptops, they have no way of removing the battery out.
And you are using A/C power (plugged in).

Beside regular charging is always better & keep your battery happy.
Glad I got this for the wife and daughter to use and check while I can always use a DVM.

Just great