Old saying if the cost is to good to be true, then it is not worth it.
1) A cheap Digital voltmeter is around $15
2) This tester will ONLY work, if it works, if the system power is on long enought to get a reading. Ie if powered on and post kicks you out in say 20 milisecs and PSU is disabled - NO WORK. IF system stays powered on long enough to provide a reading (and you can deciper it - Comments indicate very POOR documentation), I'd give it maybe a 20% chance of properly identifing the root cause.
Bottom Line ( have a preety good knowleges of test equipment) after reading the reviews - Think I'd use the Money and Buy a beer.