I have used this completely free service numerous times, and it has been effective in every case. Just copy-and-paste the item number for an auction into the form Gixen provides, and set your bid amount Gixen does the rest. Multiple (seemingly limitless) bids can be set simultaneously, which are displayed in a list beginning with the auction ending soonest and continuing chronologically.
Group items together if you want one bid to cancel another occurring at a later time, providing you win on the first one. This is very helpful if there are several auctions for a particular item that you want ending within a short time from each other, and you are not confident of winning on your first try. Why not have a go at all of them? If you do win somewhere along the line, there are no worries about a bid being placed on those still to come.
An upgrade, called Gixen Mirror, is available which raises the certainty of your bid being placed from an estimated 99.5% to virtually 100%. Generously, Gixen allows you to use the free version infinitely without being required to upgrade but, at only $6.00 for a year's service, it might be worth it just to show your appreciation.