New Twiddle

components.x-wat.js

import Ember from 'ember';

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

controllers.application.js

import Ember from 'ember';

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
With block: <br>
{{#x-wat}}
  blocky
{{/x-wat}}

Without Block: <br>
{{x-wat}}
<br>

With component-helper
{{#let (component 'x-wat') as |fu|}}
  {{#fu}}
    lol
  {{/fu}}
  {{fu}}
{{/let}}
<br>
With component-helper wrapped in a hash this works:
{{#let (hash fu=(component 'x-wat')) as |ui|}}
  {{#ui.fu}}
    lol
  {{/ui.fu}}
  {{ui.fu}}
{{/let}}
<br>

templates.components.x-wat.hbs

{{#if (has-block)}}
  {{yield}}
{{else}}
  blockless
{{/if}}

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}