As accurate as MaxMind[1], since that's what they use [2]. In my experience, it's reasonably accurate for the US, less so for other countries. MaxMind publishes some accuracy data which might be an interesting starting point [3]

That said, for any analytics use cases of this data, be aware that MaxMind will group a lot of what should be unknowns in the middle of a country. Or, in the case the US now, I think they all end up in the middle of some lake, since some farm owners in Butler County, Kansas got tired of cops showing up and sued MaxMind. It can cause odd artifacts unless you filter the addresses out somehow.

1 https://developers.cloudflare.com/support/network/configurin...

2 https://www.maxmind.com/en/geoip-demo

3 https://www.maxmind.com/en/geoip2-city-accuracy-comparison