I've put the conversion thingies on both my 1" threaded steerer bikes. The advantage is that then I can use commonly available stems from my LBS, swapping them around until I find one I like. Yet, they retain the height adjustment that's lost on threadless steerers.

I even use the Profile Design ones you pictured. They work just fine.

If you prefer to look of a quill stem and want to stick with it, Velo Orange has them, as does Rivendell.