Your referenced link shows the old standard miter gauge box joint fixture.
First, everytime you replace it on the miter gauge, you need to recalibrate it. The one I made doesn't require anything except dropping it into the guides, raising the dado head to the correct height and making your joints.
The other thing that the standard miter gauge fixture won't do is a 3/8" dado for the first notch on the sides so you can have a full length rabbet. Much stronger. You'll notice on the plans that the indexing pins are 3/8" high. If the pin on the miter gauge jig were modified to 3/8" instead of 3/4", then you could do this on it, too.
I've used the type of jig you referenced for years. Trust me, if you ever use the sled type, you'll never go back to the miter gauge style.