I think Cuba is still one of the best examples of socialist policing done correctly. They do have the added benefit of having a small population and having had a huge majority of their reactionary capitalist class flee after the revolution. Their current system is more geared towards uniting the peasant class and working class through education.

China still has a large population of reactionaries and you need some form of police to prevent them from taking power.

I think the most important thing to look at when judging China or any countries policing system is how they're utilized primarily. Who is being beaten and harassed. Is it workers? Minorities? Are the police being used as a tool to suppress the exploited classes? Or are they primarily serving as functionaries of the workers?

I think in China it's more the latter, like some of the biggest stuff I've seen is them doing mass arrests of pyramid schemes and other financial criminals.