The overall build quality of the EHD-900 AI housing is extremely good. The plastic mouldings are very strong, the hinges are over-engineered and very durable, and despite its somewhat lumpen appearance the case is well finished. The locking mechanism of the pressure latch is metal, and the various components are screwed together. It's quite a heavy contraption, weighing a substantial 578g including camera, batteries and memory card, although it will just float in water with an almost neutral buoyancy of -40g.
Since it is made to fit a specific camera the EHD-900 Ai has several features that the one-size-fits-all Seahell design lacks. On the front of the case the most obvious feature is the flash window. This is linked via a periscope arrangement of mirrors to the built-in flash of the camera inside, directing the flash light up and outwards. There is a metal slotted clip around the flash window designed to hold a small plastic plate with a hole in it (supplied). This accessory allows the EHD-900 Ai to be used with Epoque's external underwater flash unit, which is triggered via a fibre-optic cable that plugs into the hole in the plate. The metal clip can also hold a filter (not supplied), necessary when shooting in deeper water because the camera inside the housing has no manual white balance control.
The back of the housing features a full selection of buttons including the zoom control, which connect via spring-loaded waterproof links to the buttons and D-pad on the back of the camera. The buttons are rather close together and could be a bit fiddly to operate while wearing wetsuit gloves, but they are set at different heights so it is possible to operate them by touch. The controls operate smoothly, and although I was only able to test it at a depth of about three metres it was quite easy to operate underwater.
The window on the back of the housing for the camera monitor is surrounded by a substantial shade which did help with viewing the monitor in full sunlight but which seemed to serve little purpose when submerged, and in fact made it difficult to see the screen at any angle other than right in front of the face. The shade is held on by four small screws, so it should be possible to remove it without too much trouble.
The housing comes with a small selection of accessories. There is the fibre-optic flash connector plate mentioned above, a spare O-ring seal and a small tool to help with removal and fitting, a small tube of silicon sealant grease, a bag of silica gel to help prevent condensation inside the housing, and a rather cheap-looking wrist strap. There is also a pouch and wrist strap for use with the camera should you wish to use it outside the housing. As we'll see in a moment, you may not want to do that.