Lifeguard is still alpha quality and not ready for production use.
Lifeguard brings monitoring to the modern age. Some features and a brief description of each is given below:
Highly Scalable. Monitoring systems such as Nagios very quickly run into scaling issues as the number of nodes and checks increases. With Lifeguard, you simply add more nodes and computation is evenly distributed across the entire cluster.
Fault Tolerant. Lifeguard is master-less and can handle failure in many nodes.