The verdict
If you run an online store and want behaviour-driven messaging, pick Klaviyo. It gives you segments, flows and revenue per flow without building any plumbing. If you have technical people, high volumes of automation or data that must stay on your own servers, pick n8n for the work between your systems. n8n is not a marketing platform with purchase-history segments built in, so do not expect it to replace Klaviyo. A technical store team can sensibly run both. For a small B2B team with no store, Klaviyo is the wrong tool, and n8n only makes sense if somebody on the team is comfortable with servers and JSON.