Hi Gareth,
I can't vouch for the ones you've linked to but I had something similar when I owned a D40. It was okay but relied on using the IR sensor to trigger the shutter so you don't get a half-way shutter press. Not sure about the D3000/D5000 bodies but I suspect they might be the same as the D40/D40X & D60 in this matter. Of course, this only applies to when you're using the button on the grip, not the regular shutter release.
A few things leapt of the screen at me in the advert:
"Professional edition with functional buttons and dial."
There are no signs of dials in any of the photos of the grip. Certainly for the D40 there would be no use for a command dial on the grip as there's no electrical contacts in the body for it to work anyway.
"Vertical shutter with half-press function."
If this grip uses the IR port (as used with an IR remote) then there won't be a half shutter press.
"Same function as original grip."
AFAIK Nikon don't make a grip for those cameras so there is no "original grip".
Note: The above comments apply to the D40/40X and D60 but may also apply to the D3000/5000 too.
