Ember Component Input Value not updating

I've got an Ember JS component that is supposed to render a text input with a formatted date. Here is the code I currently have:

import Ember from 'ember';

export default Ember.TextField.extend({
  _value: null,
  value: Ember.computed('_value', {
    get() {
      const value = this.get('_value');

      if (value) {
        return moment(value).format('L HH:mm');
      }

    },
    set(key, value) {
      this.set('_value', value);
      return this.get('value');
    }
  })
});

called with something like {{datetime-input value=model.updatedAt}}

This renders the input fine, and I can verify via the Ember Inspector that the value property is the formatted datetime, but the actual visible content of the input remains the raw, unformatted datetime value. What am I missing?