I think you've misread the price (other posters here will confirm as much). The 180mm length is the most expensive at USD169.26. The other lengths, 170,175 (which I believe are more commonly used lengths) are USD152.33. I hope its a good bargain for you then.
I would have pulled a trigger on one, but I'm hopeless at installing stuff myself. Better let my LBS install for me and my other stuff like triggers for the price difference.
also don't forget that there will be a small price difference. when you convert pound to USD.
I don't know where they come up with the price of $152.33 but they will charge you pound instead of USD. I don't think it'll be over $160. still not a bad deal.