I've used Hammersnipe for 5 years or so.
I use it for all my bids, and until Ebay goes to a "sealed bid" format for all auctions, I think everyone should use bid snipers.
In short, it saves money by preventing bid wars.
I've never understood why people will say "My auction was stolen by a bid sniper", when the truth is the sniper simply bid higher then you were willing to pay. Plain and simple.
Other auctions use anti-sniper formats where anyone who bids in the last minute automatically extends the length of the auction my 5 minutes. I will never use an auction that has that format. The only purpose of that format is to CREATE bid wars.