They're selling an operational service that their customers can't easily replicate, even with the code.

Their product is a globally-distributed monitoring system. Running these systems all over the world, and keeping them running, is a serious operational headache. It's probably at least as complex as operating the service the customer wants to monitor - perhaps a lot more, given that most services are not globally distributed.

As long as they price below "double your ops budget", they'll remain value for money - even if the code they use is free.