i did a good deal of searching....there are MANY claims of them being legit and actualy delivering....however....
You must give them your steam username and password...... big no no in my book
Steam can BAN YOUR ACCOUNT if they find that you used this place as they are no authorized by steam to sell / give away product keys
There have been claims of the steams registered email suddenly getting an influx of spam mail after handing it over.....which means they most likely sold the users registered email address.
From what i am seeing as well, you need to pay them for a chance at winning. this would be how they make money. give away a $50 game they buy themselves from the $300 in bids they got kinda thing.
my advice would just be to stay away. like me for example, i have a TON of games i actually paid for in my steam account....i would seriously cry if it got banned....they payout just doesnt seem worth the risk to me.