I like that you can use any node framework for your sails app (like Express) which is very useful when building an application with multiple frameworks/libraries in one project! Also using bluebird promises instead of callbacks simplifies asynchronous programming quite much compared other JS MVCs out there such as AngularJS or Ember etc.. In some cases this might be confusing at first but after getting used its pretty straightforward :) not many downsides really apart from maybe being too flexible sometimes - ehm well thats just because we are all humans ;) so if everything works fine then no issues here? We were looking into different options how would setup our backend servers without having another server running rails since most things require Rails anyways right now :).