EU? There’s almost zero information on the company, no privacy policy? The only place I found any mention is the footer, “HID Global Corporation, part of ASSA ABLOY”. Assa Abloy seems Swedish but HID Global is a US company as far as a quick search goes. But without a proper company info page and privacy policy I wouldn’t consider it anywhere near a “good alternative” regardless.

3 90-day ACME certs for free. 180€/year for unlimited 90-day certs and 5 yearly ones.

That’s a pretty steep increase. I would almost be more interested in a monthly fee per cert.

I use them in some cases to avoid the rate limits on LetsEncrypt, and they have better support for some older platforms (like ancient Android versions), and I'm pretty happy so far. I have a paid account to support them, but it's not a requirement for ACME certs. It works without issue with Kubernetes Certbot, and seamless to switch between ZeroSSL and LetsEncrypt.

I can't comment on the EU part though - not that relevant in my case.

There was some subtle issue with ZeroSSL's implementation of ACME that I ran into with, IIRC, lego and domain certs and there was a ~5 year old lego open issue about it. That was a couple years ago, might be fixed, but my understanding at the time was that it was an issue with Zero's ACME implementation, so there may be dragons.

ZeroSSL aren't an EU-based alternative, unfortunately.

It's Sectigo under the hood.