Advantages of ferrite are that the material is cheaper than the correspondinging materials. That the magnet does not corrode and lasts for a very long time in tough conditions. And that it can handle a high working temperature. The disadvantage is that the strength is the weakest of all magnetic materials.
The stated forces have been determined at room temperature on a plate in polished steel (S235JR according to DIN 10 025) with a thickness of 10 mm (1kg ~ 10N). A maximum deviation of -10% compared to the specified value is possible in exceptional cases. Value is exceeded in general. Depending on the type of application (installation situation, temperatures, counter anchor etc.) the forces can be influenced enormously. The indicated values are serving as an orientation.