I've identified the model and downloaded the manual now. (Silly me, the model number was in your image.)
According to the manual the gadget has no electronics and no auto diaphragm, which means it behaves like my Olympus lens I described above. It also has f/11 as its maximum aperture, which means the viewfinder will be too dim to use conveniently other than on a tripod outside. Their comment about requiring exposure compensation just suggests they don't know about the -S screens - it is consistent with a fully manual lens on a body with the stock screen.
Because it's only f/11 you'll want to use "live view", in which you hold the camera in front of you and frame on the LCD - not all DSLRs have this. I've never used either live view or a compact, so I'm not qualified to judge, but I would think a µ4/3 camera might be more suitable if they'll let you exchange the gadget for that version. A DSLR is rather heavy and ungainly thing to hold out in front of you Sea Hunt style.
It isn't clear to me how they handle the different aspect ratios. Canon DSLRs are 3:2, not 4:3.
EDIT - looking again at their site, it may be they use the same lenses in the 4/3 version so it becomes a telephoto equivalent. Very hard to tell which model the comment applies to.