Sorry I missed this. Yes there is a free trial- right now you get 100 notifications to test while building your integration out. Also a promo on producthunt today for 20% off.
The API also has support for things like custom vibrations, urgency, icons, and action URLs. But- these are minimally supported by Safari Desktop and Safari Mobile today.
I hope Safari iOS adds support for actions and shortcut workflows when clicking a notification.
Relatively easy to work with, though I hope their OS integration will add support for more native iOS notification features like actions.
If you wanna try out native push notifications it's pretty fast to try out: https://alerty.dev