I've been trying this lens out. Firstly on a Canon D60 then on a Sony A7II via a Metabone adapter (a MkIII). Although conditions were good for around here (in the Menai Strait), they may not be considered so elsewhere! Anyway behind a Seacam CompactPort with my best guestimates for placement, the lens works surprisingly (as in very) well. It can actually focus on the dome so its close focus ability is good and focus speed (on both cameras) is fast. Here are a couple of shots:
First is at about 13mm on the D60 (single Seaflash illumination):
and second is off the Sony (vis had dropped) and is slightly cropped because of vignetting caused by the MkIII adapter although it probably will cover full frame from 13~14mm upwards.
This lens is quite cheap and from my tests it looks like its one well worth experimenting with more. More pix on Facebook.