As a PC Technician I come to this site for reference. Their results aren't always perfect, but it's because they are taking an average from many different computers. Of course depending on what hardware a particular PC has, will make all the difference. So as I said don't think of it as hard evidence, think of it as just a reference to give you a basic idea where things stand. As for their software, it's safe and decent software to use. If you want to benchmark your computer to see what score you get, just download and install the software, you get a 30 day trial with most of it. You'll be able to see the strong points and weaknesses of your configuration, and where you can improve at.
This site does a real disservice to anyone trying to accurately gauge the best hardware for their use scenario. First of all and most damning is that their is very little consistency in their rankings. Sometimes they are pretty accurate, other times they are way off the mark.
Do yourself a favor and read a few reviews from people who understand the subject. There are some great tech sites out there that break down the strengths and weakness of many different computer components. Check out sites like Anandtech and Guru3d if you want a more in-depth and accurate look at the performance of a given tech product.