Pricing: $1.25/month ($15/year) compares pretty favorably with most services I've seen (most start at $5/month or $50/year).

SMS: Most services either charge extra (~$0.20/message on average, or add a service fee for SMS notifications. Or, they only offer email-to-SMS, so you're not getting properly-formatted messages from a real phone number.

Simplicity: I'm trying to make this service as simple as possible to use. If you need a ton of special features, there are a lot of sites that give that to you—however, I just want to add servers to monitor, add my contact information, and forget about things until one of my servers goes down. Which hopefully never happens :)