This stuff is no joke! It is the best product I have ever found to control oil. It can be a bit finnicky, meaning it goes on thick and can get bally and patchy with some makeup, or feel too drying. But if you can find a technique that works for you, then this stuff is amazing. I have found you can make many moisturisers, sunscreens and primers matte by mixing this in.
Personally, I mix this with my sunscreen to create a kind of primer with SPF. I need to control oil because I wear makeup and have full workdays where I can't really touch up much, plus in the summer I cycle 40 minutes to work. Shine Stopper extends my makeup wear to 3-4 hours before needing a blot, and even then, we're just getting into glowy territory. Without Shine Stopper, I have maybe 2 hours before I've got an oil slick going on.
This has made such a big difference for me, that I think everyone with oily skin should give this a try.