I've just got one of these painted and fitted. I had to file about 1mm off the back of one of the holes to get it on the chassis, but apart from that, fitting was very easy. The only thing to look out for is to make sure the bit M12 bolts at the front cross-member do not rub against the power steering hose there. I used nyloc nuts to present a curved edge to the hose and to make sure I didn't end up with bits of brace bouncing down the road.
My car also has the 960 engine crossmember braces and the square plate fits fine with those using the standard bolts.
Subjectivity the car feels stiffer, it's noticeable even when jacking the car up. I've no idea if it actually makes the car faster round corners, but it certainly feels nicer to drive. Theoretically it should make it easier to feel the difference that other changes are making since the movement of the suspension will not be absorbed by the chassis twisting. We'll see.
DSCF1747 by
crogthomas, on Flickr
DSCF1746 by
crogthomas, on Flickr