The information in Banefulsamurai's post is almost correct, but there is one error. The "Snapshot" is 3%, not 2%. Also, Chefm is wrong, you cannot stack the same augment. I wish you could though, because 6% haste would be nice, as would Str +8.
Really is the best choice for the head slot for a multi-hit weapon skill. You cannot get +25acc for WS in any other slot, period. Yet, for all the other gear in the same slot you can get better stats with this head piece than without.
@Fairy.Leeuwenhoek: hey, this cost you only 10$/€, don't ask too much XD. How did SE manage to sell these 3 add-ons, ratio content/price is awfully horrible...