The main problem that Pagerduty solved at the time was deliverability of alerts. It was hard, and still is, to solve the problem of making sure the right people actually get the alerts. It was so expensive because they have redundant hardware all over the place with different providers, and they ran it all themselves, including SMS and phone gateways.

One of their key differentiators was that they were not built on AWS, so when AWS had an outage, you still knew about it. That also made it expensive.

With Pagerduty, you're mostly paying for reliability. The peace of mind knowing that someone will get notified when there is an outage.

This looks interesting, but from your page I'm not sure how you're better than Pagerduty.

App only notifications looks like a disadvantage to me. What if push notifications are down? What if I'm on DND?

Where is your infrastructure built? Is it on a cloud provider? What happens if that provider has an outage? If you want to build a PD competitor you have to build it on your own hardware in multiple datacenters owned by different people with different interconnects. If you haven't done that how will you stay up when your customer's provider goes down so that they know about it?