The main thing that attracted me to this is... ok you guessed it... its free!!
The software lets you monitor a single site for free and also includes an iPhone app and desktop application for your PC, which provides you with regular updates should anything go wrong. I have been using this for 2 months now... So far its been fine and showing me 100% up-time. Guess the only time i'll know if it works, is if the site goes down.
Before you ask... i'm not on a referral commission or anything of the sort!!