If you describe a person as 'good fun', it means that they are good company. They have a good sense of humour and a sociable personality, and it is fun to be around them.

It's fun that you wouldn't be ashamed to tell your Mother about ) But I've never heard of a 'good fun' personality.

When someone say you are "good fun" , it means you are someone whose company they enjoy a lot -- in the sense that you are never boring to them.