I picked up a Wallenstein thumb at my Kubota dealers a week, or so ago for $315. Mine has the two holes in the thumb support, and not three. Today I had a chance to give it a good workout on a couple of old pine stumps, a large rock, and a very stubborn Elm stump. It seems to work pretty well. I did bend the "D" ring handle on the cross pin down in the dirt against a rock I guess. Perhaps a bit more curve in the jaws, or a projection on the end of the thumb would make it easier to grasp things like the larger rock I have pictured here. Take a look at the photos, and see what you think. I'd be happy to answer any question.....
Chuck