A licence to use this hosted overlay service. €5 buys one year from the day you buy it; nothing renews by itself. A lifetime licence means the lifetime of the service, not of any person — if it ever shuts down you get at least 90 days' notice and an export of your settings and progress.
This is a small service run by one person. It is not sold with an uptime guarantee, and it depends on Streamlabs, TipeeeStream and Twitch continuing to offer the interfaces it uses. If one of them goes away, so does that feature.
As a consumer in the EU you may withdraw within 14 days. Because access is immediate, the checkout asks you to agree that performance begins at once, which ends the right of withdrawal once it has been fully performed (§ 356 Abs. 5 BGB). If something does not work, ask for a refund — it will not be a fight.
Do not use the service to break Twitch's terms, to defraud your viewers, or to attack the service itself. Accounts doing any of those can be closed, with a pro-rata refund.
The lifetime price shown is an introductory one for the first 200 buyers; after that it rises to €30. Licences already bought are never re-priced.