Hehe, well if you don't pay you can hammer snipe an 3 auctions a day. Basically you put in your highest bid and it will bid for you automatically (like eBay) however, if someone in last 10 mins bids higher than you, it will bid higher automatically for you. (Hope you understand that!)
No, its not dangerous or expensive. Its free to use and you will never pay more than what your have been outbided - for example...
If I put my maximum bid for some shoes was £15, it wouldn't bid for me until the last 10 seconds. So if the shoes in the last 10 seconds were going for £9, it would autmatically bid the next highest you can bid (like £9.50). If you were outbided again at say £10, it would then automatically bid for you £10.50 or whatever. If someone bid £15 staight off, you wouldn't win as you put your highest at £15.
(Hope you understand that! LOL)
It is really good and you usually do win auctions with it