I found it really hard to understand how this worked at first. I feel that having a tutorial would be extremely useful, show a board, describe the problem, show picking a letter, undoing it, picking the right letter, etc.
I've made a video tutorial. Check it out.
+1 on this one, there should be a tutorial with maybe a shorter word to explain how it works, this said I don't think I am smart enough for this one :D if the dots were fixed and you just had to reason on the connections, maybe, but being able to move dots left/right makes it a bit too hard at least for me. This could also be a "expert mode" thing too, have the basic mode with the dots where they are supposed to be, then expert mode making them movable