I have to say, I was hoping this would be a great solution to monitor my web design client's websites, and it absolutely is! In fact, UptimeMonster probably just saved me a client. A site I designed and have managed for years (which I've had no issues with in the past) went down the other day due to a change the hosting company made (on our VPS). For some reason, none of our other client sites were affected, but this particular client's site went offline. Within minutes, I was notified by UptimeMonster and I was able to get to work immediately to investigate and fix the issue.
This is a solution I've wanted for years! And, at this price, it really can't be beat. I highly recommend it. Don't miss out on the AppSumo deal. It's one of the best purchases I've made here. :-)