Never had an issue with this. It's not flashy, it's not pretty, but it does exactly what it says on the tin - snipes for you. Even paid for the mirror service for a year last year just to put a bit back into it it's that good.
With this for free, you can't go wrong. Set your bids, group them up if you want to possibly win one of several items, and don't worry about anything until you get an email through saying you've won or not.
Some people might balk about putting their usernames and passwords straight into it - but hey, it's got to put the snipe on for you, and I've never had an issue with my user as a result.
I personally can't fault it. Absolutely fantastic!