First of all, legally speaking, Modafinil is not a nootropic, it's a prescription drug in the USA. Also, modafinil is a wakefulness-producing agent, not a concentration/focus boosting compound, so Red Focus and Modafinil are really nothing alike.
Taking Modafinil will help you stay awake and not get tired. Taking Red Focus will help boost your concentration and focus when you need to do work.
Since Modafinil is a drug, we recommend that anyone taking it speak with their doctor about any possible interactions before taking any dietary supplements with it.
Hypothetically speaking, there should be nothing in Red Focus to negatively interact with Modafinil. So if someone were to take Modafinil at 8 AM and then Red Focus at 2-3 PM to help boost their concentration and focus, that should be–hypothetically speaking–totally fine.