Several years ago I got my Mum an Infinix phone. The default UI was painful, just really full on adware. I would change the launcher, but they kept changing it back every couple of days. One day I tried changing the default messaging app, a message popped up saying "Play Fair!" and changed the app back to the spyware-ridden default. I couldn't believe the gall! Stopped using cheap Chinese brands after that, though I doubt Oneplus would be as bad.