They’re all, perhaps with the exception of raw steel-cut oats, or plain bran, pretty simple carbohydrates, and you add sugar in the form of lactose on top to eat them. Pretty sure none of them are a net positive to health.

The UK diabetes website says they’re fine. I’m sure if you were diabetic you would be extra careful about milk, portion size though. For everyone else they’re about as low sugar as cereal gets, whether we’re talking breakfast cereal, or cereal in fields cereal.