I received a genuine D-BG4 grip for Christmas, so now I'm in a slightly better position to speculate on the DX grip.
Based on the pictures on the DX website, it looks pretty much exactly the same. The shape of the outer shell is definitely identical. I wouldn't be surprised to learn it's made in the same plant as the Pentax-branded article, using the same molds for the plastic parts. Maybe Pentax's supplier does a little direct-to-wholesaler business on the side...how much Pentax would care about this is a discussion for another thread.
Here's what all I can tell comparing the pictures to the grip in front of me:
- The housing of the grip is visibly identical.
- It's hard to tell if the rubberized overlays on the grippy surfaces are identical. Doesn't quite look the same, but it could just be that the photograph is too poor to accurately reveal the texture. I'll say it could go either way on that one, but I'd expect a lower-quality material.
- The recessed holes for storing the contact covers from the grip and the camera look identical. Does this grip even have a protective cap?
- The screws on the top and bottom are all in the same place. This is no surprise, as it goes along with appearing to be cast from the same mold.
- Who knows about the electronics? Presumably it functions similarly, but there's no way to tell if it's got identical "guts" or merely equivalent ones.
- The battery trays look indistinguishable from the genuine ones (except lack of weather sealing, see below). The only possible difference might be that the screws in the DX version of the AAA tray look black, while the Pentax screws are silver. I can't say for sure if that's real or just an artifact of the lighting and angle of the photograph. Sort of insignificant anyway.
- The screen printing on the buttons isn't the same. It's a reasonably close facsimile, but the lettering and icons are just a bit different. That's where it most visibly becomes a cheap knock-off.
- The DX grip is missing all the weather-sealing visible on the mount side of the genuine grip. On the "real deal", various parts on the mounting face of the grip are surrounded by a foam rubber obviously meant to give the grip weather-resistant properties. The contact pin cluster, as well as the push-switch next to the pins, are ringed by foam rubber. That's missing on the DX photo. Similarly, the holes at the four corners of the grip's mounting face, as well as the oval depression next to one of the metal locating studs, are filled with foam rubber on the Pentax model. Not so for the DX model. Finally, the Pentax battery trays each have a foam seal around the surface which seats against the opening in the main grip housing, the DX trays don't So it's clear that while the Pentax grip is sealed well against dust and moisture...the DX grip doesn't provide the same protection.
So it looks and probably feels much the same as the real article. It looks a bit cheaper because of medicore label printing, and it won't have the same weather resistance as the genuine grip. But I must say that if I were buying one for myself (and hadn't been lucky enough to get one as a gift), I might be inclined to give the Deal Extreme model a go at 1/4 the price.