I really like mine -I think it was $15 including shipping. I think you'd have to whack it pretty hard (and then maybe other bike parts would break anyway) before you'd break the bosses. I can't remember if I used the bolts provided to attach to the brake bosses, or if my bolts were long enough already.

While I'm not a big fan of attaching a rack to brake bosses, I think for what it works for -i.e. 5lbs or less -it's fine. Further, I always put the load as close to the steering tube as possible. For the flexibility it offers given the price, I really do like it; it allows me to swap about 5lbs of weight from front to rear to give me a nice balanced bike.