That's for posting this! I'm one of the engineers on the team who built On-call, so if you have any questions about how we did it (like how we handle redundancy, observability, etc) then I'd be well up for answering.
It's been an intense 9 months of work but think anyone on-call is going to really love this.
Its too expensive, very flashy and unless you go for the enterprise plans, any team over 20-30 people are gonna feel very restricted. It looks better than PD but is a very similar poison.