Our experience with Backbone, was that the majority of code in your models and views is about keeping the two in sync. i.e. if a field on a model changes, how to update the element that the view controls in the most efficient possible way. We experimented with several methods of handling data-binding (two-way at the time) for us, but weren't satisfied with any of them.

I was building a particularly complicated content editor with Backbone, and was getting frustrated. So I spent the next morning learning React, then re-implemented the whole thing that afternoon. All the complexities I was grappling with disappeared. Obviously there were new challenges to replace the old ones, but we've found it's much easier for someone to pick up work on a React project than it ever was with Backbone.

To start with we were using Backbone models with React views, but now we just use a flux implementation (Fluxxor), and don't bother with much else. Our client-side JS stack is essentially React, Immutable, Fluxxor, superagent, moment and mousetrap, with only the first three being core ingredients.

This repeats my experience too. Backbone gets nasty too soon: nested entities, pagination, invalidation, caching have to be ad-hoc ugly solutions because Backbone is just too rigid where it better be flexible, and too flexible where it should have been rigid.

We gradually moved from Backbone to React+Backbone, and finally to React+Flux. It's been amazing since.