Formidable is awesome and robust but may have a high learning curve. I have used it for really incredible purposes like submitting real estate listings through a form, tracking customer orders (CRM), mobile app trouble tickets, contact forms, page and post creation, etc...
What I will say that can be challenging, is that the updates may change functionality (usually for the better).
What you can do with this plugin is amazing, and you can literally be a designer that builds web apps because of this plugin.
The warning from the first sentence is that YES this plugin does an unlimited amount of things, but it also DOES TAKE A LOT OF LEARNING. So stop being afraid to learn new things, and realize that people like Strategy 11 have gone to extreme lengths to empower non-developers!
Benefits of this plugin with Pro account: unlimited installs, unlimited upgrades, unlimited support.
Drawbacks: difficult to roll back to previous versions, high learning curve to learn how to completely use it.
Forget the drawbacks! Get on it and grab this plugin in the Pro version and get to realizing what you web designers can do in terms of functionality with a website!