I've got both albeit the big ones I have are authentic. My KF5 mini pisses juice if I open airflow more than about half a turn where as the big ones need 2 full turns as normal and this is having checked and changed some of the seals. No doubt just an idiosyncrasy with mine!
As said though a KF3 mini with a steel tank and SteamTuners drip tip (that fit the only SXK KF3 clone I have) gives a better MTL vape and holds 3.6 ml of juice, 4.5 if you go for the bulbous steel tank, so more juice and smaller than a KF5 mini!