I've been using Knock while it was in beta for a few months now, and was actually very impressed! Implementing notifications from scratch can be very difficult, and I was pleasantly surprised by how smooth Knock workflow is. It has pretty much every feature an engineer might need, including: templating, cancelling notifications, in-app notification feed, scheduling future notifications, out-of-the-box integrations and much more.
Knock is also extremely reliable, I don't think we ever had even one issue with Knock itself.
A suggestion for a couple features that I would find extremely useful:
1. Have a declarative way to define Knock workflows (eg with a terraform provider).
2. Provide a way to run automated tests against Knock (without setting up a test mailbox).
