Knock is not just "more notifications"
Knock belongs in the architecture conversation. It gives teams a system for notification types, user preferences, templates, channels, provider routing, and in-app feeds. That matters when notifications are part of the product experience.
PostHog Workflows belongs closer to analytics. It starts from behavior and triggers an action.
Both can send something. Only one is designed to be the notification layer.
When PostHog Workflows is enough
PostHog Workflows is enough when the notification is a side effect of analytics. A high-intent account should trigger a Slack alert. A user who misses activation should receive a simple email. A cohort should sync to another destination. A webhook should fire when a product signal appears.
The value is in acting from the signal, not building notification infrastructure.
When Knock is the better choice
Knock is better when notifications need product-grade rules. Users may need to choose channels. Some messages should batch. Some should fall back to another provider. Some should appear in an in-app inbox. Engineering needs one API instead of scattered notification code.
At that point, PostHog Workflows can still be a trigger source, but Knock should own the notification system.
Where Sequenzy fits
Sequenzy is simpler by design. It is not trying to be a general notification API. It is for SaaS email workflows: lifecycle campaigns, transactional messages, billing notices, onboarding, activation, and reactivation.
Practical rule
Use PostHog Workflows when the notification is an action from product analytics.
Use Knock when notifications are part of the product platform.
Use Sequenzy when customer email is the thing that needs a home.