Last service I used was esnipe.com, but they charge min 25 cents or 1% up to max of $10.
I liked the idea of setting my max bid in advance, without showing that I was even bidding on an item, and my bid was always placed about 5 seconds prior to close. When other bidders see people bidding, they very often increase their own bids, and some people panic in the last moments of an auction and bid more than they really want to. Sniping avoids that.
I might try this new service, but I sure don't want to be called on MOST auctions, maybe if I was bidding for a kidney etc.