I like what GitHub and Jetbrains are doing, where you get Copilot and PyCharm for free as long as you're a maintainer. They keep renewing my license.
A 6-month trial isn't showing appreciation for OSS any more than "first crack hit's free" is showing appreciation for what a good person you are. It's just "you look like a promising customer".
It's a spectrum, right?
It would be showing greater higher quality appreciation to offer an ongoing benefit.
But there is some benefit to giving maintainers a generous trial length with your offering. 6 months is certainly long enough to see how well it does or does not incorporate into your project.
It just so happens we almost all universally love the offering.