Hello liam,
Yes, you can select what you want us to clean or not. The product at the point in your screenshot, is still not licensed. You can't run a clean of your PC until you buy it. Once you buy the product and click "optimize my PC" it will boot (restart) into Linux and run through the cleaning of your PC. At the end of that, you are able to see a console of what was found and you can customize items so they won't be cleaned if you wish. At the moment, this is the only way of customizing/selecting what to clean/not clean.
However, we are going to release a new version of GrimeFighter in a couple months that will show you all the details up front.
Hope this helps,
Davidek