9 series Climbers are designed to handle conditions that are heavy duty. They will handle consistent use in thick, heavy, rough grass that is damp or even with high moisture content. Even thin saplings up to 25mm can be mown down. Naturally, obstacles such as tree trunks, rocks and other solid objects should be avoided.  7 series Climbers are for use on smaller properties where the conditions are more moderate and less extreme but like all machines hitting solid objects can cause damage to the machine.