The problem with having 2 sniper services bidding for the same object is that they will both put in your bid and will both see that you won so you will have to pay both sniping services because they both put in your bid and you won the item. They do not know if you already had a bid in or not. If this is something you really want and are willing to pay both services for I see no problems with using both services but I have had good luck with the one in your first link.
See this question in the auctionsniper faq.
http://www.auctionsniper.com/faqbasics.aspx#basics15 
