Can share a few things. First, China is a bad country for privacy, as the government could compell to install backdoors. Second, it depend wheter you purchase the chinese version (ROM) or the international ROM. Third, I purchased a Xiaomi (Chinese ROM) and the security updates come in quarterly batches or so. Fourth, this Xiaomi ROM need me to complete ID verification to unlock it to put another OS. That being said, Xiaomi is the only major OEM that allows fastbooting AFAIK. Five, Xiaomi had a scandal where their browser sent some data home, but after a backlash they “fixed” it. Six, Xiaomi permissions management is more fine-grained than Samsung
For any mainstream phone, use Universal Android Debloater Next Generation to remove the bloatware. I am actually writing a guide on this.