The decision starts with the data model
Klaviyo is not simply "PostHog Workflows with more marketing features." It is a commerce automation platform. Its best work happens when the customer record is tied to store behavior: viewed products, carts, orders, discounts, average order value, repeat purchase, replenishment timing, and SMS consent.
PostHog Workflows starts somewhere else. It sees the user through product behavior: signed up, invited a teammate, used a feature, abandoned onboarding, crossed a usage threshold, or showed expansion intent.
That difference matters more than the feature checklist.
When PostHog Workflows is the cleaner choice
Use PostHog Workflows when the automation is a direct response to product behavior. If a user has viewed the dashboard six times but never connected data, the audience logic already belongs in PostHog. If a high-value account hits an error path, a Slack alert or webhook from PostHog keeps the work close to the signal.
The strength is proximity. There is less translation between "what happened in the product" and "what should happen next."
When Klaviyo is the obvious choice
Use Klaviyo when the workflow is about revenue from a store. Abandoned cart, browse abandonment, back-in-stock, post-purchase education, cross-sell, replenishment, holiday promotion, and winback campaigns are Klaviyo territory.
Those flows need product catalog context, order history, customer value, discount strategy, SMS, and revenue reporting. PostHog can track events, but it is not trying to be the command center for ecommerce retention.
Where Sequenzy belongs
Sequenzy is for SaaS teams that recognize neither side is quite right as the permanent email home. PostHog should keep product analytics. Klaviyo should stay in ecommerce. Sequenzy owns the SaaS email work: onboarding, activation, billing, dunning, transactional notices, churn prevention, and reactivation.
Quick rule
If the phrase is "cart", "order", "catalog", or "repeat purchase", start with Klaviyo.
If the phrase is "feature usage", "activation", "cohort", or "product behavior", start with PostHog Workflows.
If the phrase is "trial", "subscription", "invoice", "upgrade", or "churn", compare Sequenzy beside PostHog.