Why Not ...?

FormState

• Requires controllers or state to track fields' values (i.e. You need to create TextEditingController to get TextField value).
• Requires a separate state to assign API errors require to fields.
• Requires extra state to track form's status (Loading, Invalid, etc.).

Flutter Form Builder

• Requires a separate state to assign API errors require to fields.
• Requires a key to be able to access form.
• Requires explicit calls for save and validate.

Reactive Forms

• Requires a lot of boilerplate (due to the model-driven approach).
• Complex and has a higher learning curve.

BLoC + Formz

• Requires a lot of boilerplate, really a lot!
• Complex and has a higher learning curve.
• Formz doesn't get any more updates.