The modules simply slide in to the holder, a much better system than the D200 grip which had fiddly plastic catches that had a tendancy to break.
With the EN-EL4(a) battery held in by the BL-3, or 8*AAs in the holder, the D300 can on CH shoot happily at 8fps.
To install the grip, just pull off this piece of rubber from the bottom of your D300 (it's replaceable)
put it in the recess in the grip designed to hold it. You can put the original EN-EL3 battery inside the camera, as well as the one in the grip, if you want, but to change it you do need to remove the grip.
Screwed onto the camera, and you can see the inside of the grip - lots of reinforcements, it's not the magnesium build of the MB-D10, but it's damn strong. There's a big plate of metal along the bottom where the tripod screw is, and the door closing on the battery inserts is a million times better than the closure on the D200 grips.
Controls wise, it has a D pad, rear aperature wheel and AF-ON. The D pad is great, I prefer it to the one on the D300 body!
It's got a decent half stage shutter release button that feels the same to use as the D300's, and a lock switch around it that can disable all the controls on the grip. It has a shutter speed wheel on the front too - it's basically the same controls as the body.
The wheels give slightly more resistance than the D300 ones to turn, but not much. The af-on button is hard, unlike the slightly rubberised ones of previous grips.
The grip fits flush to the camera, no wobble or anything whatsoever.
For less than £50 posted, I'm very happy with them (once the first arrived and I was happy, I ordered another), they come with all the accessories, 8fps is amazing for the times when you need to use it, and I certainly won't fuss too much over them in the rain or in terms of how I treat them, they're well built and a great alternative to the MB-D10 if you're feeling the strain - it would've been an extra £300 odd for me to use the official ones so it was a 'this or nothing' scenario.
Watch out for the 'non pro' versions that are a bit cheaper, but have built in battery chargers and junk like that but no aperture wheels etc...