I wanted to get this because I seem to be the only "car guy" in the household and amongst extended family (some 20+ people all in Dallas).I do all of my own car work, and could easily do simple battery voltage checks with a multimeter, but a device like this is important, because it measures amps correctly (and simply), something you don't want to do with most multimeters without calculating the proper size resistor to use inline or risk frying your multimeter.  Basically, this is a device designed to measure automotive voltage, plus check cold cranking amps, cranking amps, and load testing.The 3 stars is mainly for the usability.  First, the display (the most important thing!) is hard to read because it uses large LED bars to write out the words.  Let me explain - the first test is the battery test.  When you select the battery test, it reads "baFF" rather than "batt" only because the manufacturer chose to use a very simplistic display that doesn't have enough "bars" to create easy to read words.  It's like trying to make words with a calculator if that makes any sense.  (I will try to upload a picture later)Next, of all devices that truly need a carrying case, this one does, if only to hold the instruction manual.  It is not intuitive to use without the manual (primarily because the words are very hard to decipher or read).  There's a "glossary" on the back, but it doesn't include everything, nor the steps for each of the tests, if it DID, I would've added 1 more star.Then, on top of that, the manual somewhat confuses you a little in determining what type of battery you have.  For example, for battery types you must choose from the following:SLI - Starting/Lighting/Ignition Flooded batteryFLAT - Traditionally shaped AGM batteriesSPL - AGM-designated spiral wound batteriesGEL - Gel cell batteriesNow of the 4, what type of battery do you have???  I checked 3 cars and none have any of this written on the battery themselves.  I can only assume SLI makes the most sense.  Ideally, this would be explained a little better or use "Conventional, Marine/Deep-Cycle, Maintenance Free" wording instead.Overall, I feel 3 stars is fair for the usability - the item still works and seems to validate known good and known bad batteries and charging systems, but don't lose the instruction manual and good luck being able to read the too-simplistic screen.