You have a great question which is should I use BaaS proivders to make my own application, mroeover how can I trust the backend provider to support my scale and my needs. I had the same concerns, but than I encounterd Backand . Backand is Baas that works the best with AngularJS and Ionic, free forever if you sign-up now and very open for your needs. Backand proivde you with advanced data models (and you can also keep the credentials for yourself) and various of features. Check out their recent blog post about the intergration with ionic- http://blog.backand.com/the-ultimate-stack-for-mobile-apps-ionic-backand/

I personally use Backand as they are the only backend as a service that is tailored for my angularjs applications.