I think the differences are-
1. retirement age is generally 65/66, not 60
2. May have lesser sick leave entitlements
3. Can engage in limited political activity?
4. They cannot participate in internal competitions for promotion to established positions
I haven't see that term used for a very long time; from what I recall it used to mean someone who held a pensionable position.
So if you were non-established you would not be in a pensionable position. I would guess in the modern context that would be someone who was (for example) employed on a contract or temporary basis.