I've found the app to be very helpful as a refresher. If you need a more core understanding of some of the more complicated topics such as circuitry or logarithms / systems of equations / trinomials, I would definitely recommend you search your friends and connections for a good math tutor that is willing to coach you. It never hurts to have a seasoned electrical engineer in your field walk you trough some real examples as well. Already worth the $20 if you bought it from the Apple App Store.
My $0.02