Shorthand computed properties

Can anyone please explain why these don't evaluate to the same thing?

Ember.ArrayController.extend({
    maxProducts: 5,

    hasMaxProducts: function () {
        return this.get('model.length') === this.get('maxProducts');
    }.property('model.length'),

    shorthandHasMaxProducts: Ember.computed.equal('model.length', 'maxProducts')
});

I'm using the hasMaxProducts property in a handlebars template successfully, and if I try switching to the shorthandHasMaxProducts property, I don't get the same results, nor does it seem that this property ever updates. This should happen when I add another model to the array collection. I've also tried computing with:

Ember.computed.equal('model.[]', 'maxProducts')
Ember.computed.equal('model.[].length', 'maxProducts')