As its name implies, System Checkup scans your system in search of issues that need to be fixed. The program performs a set of 8 tests, namely, Internet speed, Memory levels, Startup speed, Registry issues, Security holes, System clutter, Internet clutter, and Shortcuts check, detecting the problems in those areas that may affect your system's performance.
Albeit the program is free and light, and performs swiftly, it only detects the issues on the aforementioned areas, but does not fix any of them. Instead, it urges you to purchase System Mechanic, which is a pay-based program sold by the same developer. Thus, it is fair to say that this is not really a system optimization program but a marketing tool, since its main goal is to sell you another program. In any case, you don't need it to simply detect issues in your computer; if you purchase directly System Mechanic or any other system optimization program, it will detect these issues and will fix them as well. In short, this program is nothing more than a waste of time and resources. You could try using it at your own risk.