I think cautious optimism is warranted, with the needle moving more towards the optimism side than the cautious side. He has been successful in his role at a big time program. Key has been successful with these types of hires in the past. Obviously, there are no guarantees, but it looks like a good hire.
*Edit to add that I like the fact that he was a successful special teams coordinator in the past as well. Still no guarantees, but it's a plus that he's had that experience moving from a position coach to a DC.