I've been using MobX on a quite large and complex React app for a few years now and I have no regrets. The key, as in all programming, is to make your (observable) state as small as possible. You shouldn't have observables that are derived from other observables; you should have computed values. You should use reactions sparingly and almost never use them to mutate other observables. Etc. MobX lets you treat state as state and then get all the benefits of memoization and reactivity that you want, for free. It only gets hairy when your state itself gets needlessly hairy.