I could not find any treads on this relatively new Olympus prime lens, but it is worth considering for its wide aperture, useful focal length and close focus (25cm, compared to 30cm for the 25mm prime from Panasonic/Leica).
On my old Canon DLSR, most shots used the 100mm macro, 35mm F2, and 60mm macro, in that order. My new Oly EM-5 has a 60mm macro that is equivalent to 80mm on APS-C, neatly in between and replacing the two canon macro lenses. So it made sense to get the Oly 25mm f1.8 as the equivalent of the canon 35 f2. On the Ikelite Canon housing I used a different port for the 35mm. Fortunately, the Oly 25mm is perfectly happy in the Nauticam 60mm macro port with no vignetting. Obviously there is a lot of air space between lens and port but every extra cm of air is one cm less water so I am not complaining. The 12-50mm kit lens, again in the same port, rounds out the set for now and has to do duty for WA and big fish.
A week from now I should have the first UW pics from it.