i've been using an sg1 grip for a short while now.
first thing is that it obviously doesnt feel as sturdy as the rest of the camera, due to it being of a slightly differnt plastic and obviously hasnt got some kind of metal substructure, especially in the part that goes up the side.
i think it could have done with more 'registration'/attachment points [not that there are any on the camera though..] but, as it is, its great!
fits easily, and it does exactly what it was designed to do.
its obviously never going to be as functional as a full proper battery grip [no extra power, card storage, secondary dial controls] but its fine for what it is [and the price it is].
in use it is fine, and frankly its never been off the camera since the day it got on there.
amusingly, sighting of it gives rise to double-takes and questions of 'got a new camera?', and i suppose it bulks it up as a 'pro' camera lol
but its great, fits ok in the hand, and luckily my bags are just big enough to still take it with the grip on.
the rubber pad is a nice thing to have on it as well.
overall, as long as the price is reasonable, its a great addition to the camera, makes it stand out, and gives you an extra way to hold it when taking portrait shots.