Flutter dart design pattern - form data manipulation

Which is the better way to manipulate form data ? With immutability (with finak keyword on property models) or not ?

Model class immutable:

class Contact {
  final String id;
  final String name;
  // many fields 
  Contact({this.id, this.name});
}

OR Model class without final keyword :

class Contact {
  String id;
  String name;
  // many fields 
  Contact({this.id, this.name});
}

---

The model class Contact is loaded from database in this dummy example;

Here I use Contact model with immutability (with final keyword), and make a copy of the Contact, for every attribute change state:

...
Contact contact;

@override
  void initState() {
    // load from database
    contact = Provider.of<ContactProvider>(context, listen: false).findContactExample();
    super.initState();
  }
...
Form(
  key: _form,
  child: ListView(
    children: <Widget>[
      ....
      TextFormField(
        decoration: InputDecoration(labelText: 'Name'),
        initialValue: contact.name,
        onSaved: (value) {
          // make a copy of contact for every attribute change
          contact = Contact(id: contact.id, name: value);
        }
      ),
      ....
    ],
  ),
),
...

OR here I use contact without final keyword, and changing property directly in the object, without make a copy.... changing object state.

...
Contact contact;

@override
  void initState() {
    // load from database
    contact = Provider.of<ContactProvider>(context, listen: false).findContactExample();
    super.initState();
  }
...
Form(
  key: _form,
  child: ListView(
    children: <Widget>[
      ....
      TextFormField(
        decoration: InputDecoration(labelText: 'Name'),
        initialValue: contact.name,
        onSaved: (value) {
          // changing object state
          contact.name = value;
        }
      ),
      // .... there are many field 
    ],
  ),
),

...