I just picked up an On Glass adapter for my 554 and am totally blown away by how good it is. I had previously been using a Phone Skope adapter with the universal lollipop and finally got to the point where I quit trying to use it because it was such a pain to center the lens and keep it centered when twisting on the the adapter.
The On Glass, however, is a dream! It pushes onto to the eyepiece at whatever orientation I want, then the phone snaps into place dead center every single time. It also doesn't require a specific case for your phone. I'm giddy over this thing.