I have used the Inon macro port with the magnetic ring and it has some upsides over the Athena port. First is cost, they are both very robust and well made ports but Inon has the better price. Most important is that the Inon port only requires one gear, which will work with ANY housing with the Olympus port mount. This means that you can use the same gear to drive the 50 mm macro lens, 50 mm + 1.4X tele converter and 50 mm + 2X tele converter. It can also be used with the Olympus housings, the Nexus E-3 housing, SeaTool E-3 housing and any other housing that comes along with the Olympus port adapter.
With the Athena port a different gear is required with each lens combination and each housing manufacturer.
The magnetic focus is a bit sloppy (to fine tune) compared to a fixed gear but I found myself using manual to reach fully extension of the lens more than anything else because AF works very well with this lens. It begins to slow only with the 2X tele converter and diopters.
Both ports have the 67 mm threaded end for the addition of diopters and the Athena ring flash.
Phil Rudin