The first version above was taken with a 16mm prime lens (24mm in old money), and the second was taken from the same spot but with the fisheye adapter added. Not 100% sure what this equates to but I think it's around 10-11mm (15mm full-frame equivalent).
The distortion in the wider version was corrected using Photoshop's Adaptive Wide Angle filter before being put through some further editing to enhance the level of dreichness in the shot.
The adapter's a cheaper option than any dedicated fisheye lens I've looked at (barring a few far eastern fully manual ones). There's a bit of softening near the edges , and some CA can creep in, all that can be fixed somewhat in post, but overall I've been really impressed with the results from the combination.
I do like a bit of fisheye me.