Hummm. I got one opf them from my local bike shop and its exacly the same as the one at bikedock.
I am on my second on in about 1 - 2months becuase the pin thing that goes behind the mech hanger poped out and something else came out with it.
I am on my second one now and it has lasted me about a month and it seems to be fine at the minuite apart from that where the chain goes round on it the part what is under it what keeps the chain on its bent somehow.
I say wait and dget a surly one or get it if you are desprate
Otherwise dont next time i am going to get a fresh products one