Mixins vs Extends - Same behaviour

components.a-component.js

import Ember from 'ember';
import FooMixin from 'app/components/mixins/foo-mixin';

export default Ember.Component.extend(
  FooMixin,
{
});

components.b-component.js

import Ember from 'ember';
import FooMixin from 'app/components/mixins/foo-mixin';
export default Ember.Component.extend(
  FooMixin, 
{
});

components.child1-component.js

import Ember from 'ember';
import ParentComponent from 'app/components/parent-component';

export default ParentComponent.extend({
});

components.child2-component.js

import Ember from 'ember';
import ParentComponent from 'app/components/parent-component';

export default ParentComponent.extend({
});

components.mixins.foo-mixin.js

import Ember from 'ember';

export default Ember.Mixin.create({
  foo: 'bar',
  bar: [],
  
  actions: {
   	addInput() {
     	this.get('bar').addObject({}); 
    }
  }
});

components.parent-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  foo: 'bar',
  bar: [],
  
  actions: {
   	addInput() {
     	this.get('bar').addObject({}); 
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

<h1>Mixins</h1>
{{a-component}}
{{b-component}}
<h1>Extends</h1>
{{child1-component}}
{{child2-component}}

templates.components.a-component.hbs

<h3>Component A</h3>
{{#each bar as |item|}}
	{{input item}}
{{/each}}

<button {{action 'addInput'}}>Add</button>

templates.components.b-component.hbs

<h3>Component B</h3>
{{#each bar as |item|}}
	{{input item}}
{{/each}}
<button {{action 'addInput'}}>Add</button>

templates.components.child1-component.hbs

<h3>Child 1</h3>
{{#each bar as |item|}}
	{{input item}}
{{/each}}
<button {{action 'addInput'}}>Add</button>

templates.components.child2-component.hbs

<h3>Child 2</h3>
{{#each bar as |item|}}
	{{input item}}
{{/each}}
<button {{action 'addInput'}}>Add</button>

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.9.0",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {}
}