To set or get the checked property of a cell control then use the Checked property.
This property has no effect on cell types other than CheckBox cells.
If you are working with 3 states (Checked, Unchecked and Mixed state) then use the Value property.
The Checked property vs the Value property:
State - Checked - Value
Unchecked - False - 0
Checked - True - 1
Mixed state - True - 2