Having played around with fisheye lenses in the past, I thought I would treat myself to the new TTArtisan 7.5mm f2: to fit my Canon M mount cameras. The lens is made of metal and available in most APS-C or M4/3 mounts.
To make the most of the new lens I also tweaked my M3 Landscape Bracketing Script, so it can use the manual TTA fisheye lens in exposure survey, auto-ETTR and exposure bracketing modes.
With a focal length of 7.5mm you most probably will never need to focus bracket, but if you do, ie to access the minimum focus distance of 125mm, then the DoF scale will allow you to manually focus bracket. Because of the focal length, you will only need a couple of focus brackets to cover the full depth of field.
Image quality is as you would expect on a $150 lens, ie acceptable, certainly for web image use.
As for post processing; the only difference between processing a fisheye and a non fisheye is whether to defish the image: an artistic choice.
As an example, here is a non-defished test capture from the lens:
After defishing the image, the result looks like this:
Defishing above was carried in DxO Perspective Efex, although I could have used FishEye Hemi or Photoshop. All post processing was carried out in Lightroom.
Bottom line: a cheap lens that is fun to use.