My verdict: it's a gadget, I prefer Google Calendar.
Notion Calendar (formerly Cron) has a beautiful Notion-style interface. It's elegant, well designed, pleasant to use.
But apart from the UI which is pretty, I don't see any major value in it. It's an elegant wrapper, but functionally, it doesn't add anything more than Google Calendar for my use.
What I like less: it's purely cosmetic. Features are identical to Google Calendar, with fewer third-party integrations. Notion sync can be confusing.
My advice: if you're a die-hard Notion fan and want everything in the ecosystem, try it. Otherwise, stick with Google Calendar - it's the standard and works perfectly.