O&O SpeedCheck simulates data reading by your Windows system in a fragmented and defragmented hard drive, no real data is ever written to the drive. After the test, which last some minutes, you will be shown a comparison bar chart of the two test times, I would not call this software a benchmark because it doesn’t give you too many details other than the possible increase in speed by using a properly defragmented drive.
You do not need to install O&O Speedcheck to run it, only administrator rights. This program is a bit confusing as it might give the impression that you need to defrag your hard drive when everything is fine, O&O SpeedCheck does not measure hard drive defragmentation level, it only shows people the speed increase they can get by defragging their hard drive and the reason why a hard drive should be defragmented often, the main point of this software is to convince people to defrag their drives and show the theoretical speed one can get from that specific drive, which not only depends on disk defragmentation, but also on system hardware. O&O offers you a 30 day trial of their defragmentation software once you close O&O SpeedCheck, it appears to be a tool to push O&O own defrag software, which can be easily ignored and would be fine as long as their freeware provided detailed data other than a simple percentage number.
The only use I see for this tool is for presentations at IT lectures, if you are a home user I would give it a pass unless you still need to be convinced that defragging a hard drive really makes a difference.