How they really differ
beehiiv is optimized for the publishing loop: write, grow the list, earn from the audience. Systeme.io is optimized for the selling loop: capture a lead, follow up by email, deliver a product. Running a media brand on a funnel tool, or a course business on a newsletter tool, tends to expose the gaps.
Both have a free plan with limits, so you can test before paying. beehiiv's paid tiers scale mainly by subscriber count. Check each pricing page for current contact and feature limits.
Using both
A reasonable split for some creators: a beehiiv newsletter for audience growth, and Systeme.io only for the paid course or product behind it.
The verdict
Newsletter-first: beehiiv. Product-first, with courses and funnels: Systeme.io. If you are unsure, start free with whichever matches the thing you plan to sell first.
Want the full write-up on each? Read our beehiiv review and Systeme.io review.