The founder version of the decision
PostHog Workflows and Loops both feel like tools a technical founder could like. Neither starts with enterprise ceremony. Neither asks you to accept a giant marketing suite before sending useful email.
The decision is about where you want to live every week.
If you want to live in PostHog, build the workflow there. If you want to live in an email tool, use Loops.
Why PostHog Workflows is tempting
The event already exists. The cohort already exists. The funnel already exists. You can build the workflow where you noticed the problem. That is a big advantage.
For example, if you discover that users who do not invite a teammate in the first day retain worse, you can build a simple nudge from the same product context.
Why Loops is tempting
Email is not only a trigger. It is copy, design, subject lines, unsubscribe behavior, broadcasts, lifecycle sequences, and customer communication history.
Loops gives that work a cleaner place to happen. For small SaaS teams, that can be enough reason to add one more tool.
My recommendation
Use PostHog Workflows to prove the lifecycle idea. If the message becomes part of your actual email program, move it into Loops or Sequenzy depending on how deep the SaaS lifecycle needs to go.