I bought this to verify the charging current on a USB device that has a design flaw where a lithium ion battery is charged at an very inappropriate rate on some of the units sold-depending upon where the battery in each particular unit was sourced. For simple USB voltage and current measurements it appears to work well. No convenient way to verify accuracy. The minuses: no manual so it is left to the user to figure out some of the other features. Also some of these default to Chinese for the user interface. Thanks to the Sparkfun community that pointed me to a youtube video explaining how to change the language setting. In a nutshell, as you are plugging it in to power hold the tiny button above and to the left of the screen. As it powers up a menu will appear. As long as you hold the button in the unit will slowly scroll through the 2 or 3 language choices. Here is a link to the video: https://www.youtube.com/watch?v=99qP7rXDOyU Please note that the unit shown in the video will look different from the one sold by Sparkfun. As soon as you get the unit into a language that you can read I recommend pressing the help button. The help screen is pretty basic but helpful. I would have given this 3 stars, however it comes in a very nice tin for storage. Like an Altoids tin but with a window.
Edit: Exploring this device further it seems that most of the other functionality is pretty straightforward. It has some graphing functions that seem to work as expected, although you may need magnifying glasses to make sense of the graphs, they are pretty tiny. I am not sure if there is a way of getting the data out of the device, there is a microUSB IN that is not matched by a corresponding output.

Does a great job of telling you what's going on with regards to power, highly recommend if you need to figure out what kind of power is being supplied or drawn from a USB port.

I bought a couple to verify power brick capacities. They are doing that job well enough. I have no real need to measure the resistance of cables but maybe one day. The trends are pretty useless to me so far but add a gee-whiz factor. Between the manual and contextual help I have 80% of my questions answered. It does the job and has a fancy screen. If that isn't worth 4 stars, what is?

It's the best product of this type I have seen. I haven't tried all the features, and probably never will. (I don't need to save data or make plots.) But, basic measurements are quick and easy. The variety of USB plug types is nice.

This product is an exceptionally useful tool for anyone building products that utilize a laptop to power a product. It paid for itself the first time we used it.

Instructions referred to a "reset" button but this button is not identified on the user information on the web site. The unit does not respond to attempts to move through the modes. Terrible, terrible waste of my time.

I got one of these last year and it was great, for a while. One day it just stopped turning on. I still have it but it's basically a little brick with USB ports. It might be good for you but plan ahead for how you'll recycle it, because you'll probably do that not too long after getting it.