At Nuclino we're very happy with MobX and I would say that it is definitely suitable for complex projects and that it mostly depends on the overall architecture that you choose. MobX is rather unopinionated and there are many ways to work with it. You can even use it in a Redux style architecture if you want! In the end it all depends on your requirements and preferences. For us, choosing MobX was key to building Nuclino the way it is today as there are a few key features which would have been much harder to build with Redux.