We have applied EmberJS to a fairly complex application backed by Rails backend. We had to deal with complex JSONs delivered by backend which were schemaless MongoDB documents. At lot many places we had non RESTful Rails controllers. So when we started with EmberJS we had a worry the documentation was not proper, there were very few reference projects. After a few weeks of thrill and steep learning we settled on with things. We have applied a lot of functionalities offered by Ember to our code. Migrated from router from old to new api of pre 4. But we feel in our team it was right thing to apply Ember. The way overall MVC imposes structured programming, the way HTML is seperated from JS, the way ember data can have serializer and adapter customized, two way bindings all of it had been useful. We struggled at few places with deep nested JSONs in hasMany/belongsTo relation in embedded JSONs. But doing workarounds were easy. We used fixtures to hasten development while backend was not yet ready. All in all we believe that we made a good choice to stick with Ember, though it looks difficult to comprehend on the start but thats also getting better with time.