That will work just fine for this specific value list, but patterncount can fail with some sets of values in a checkbox field.
Example: If you have both the values "apple" and "applescript" in the value list for your checkbox field,
Patterncount ( Table::CheckboxField ; "apple" )
will return a nonzero value (True) when applescript was the actual value selected.
Not IsEmpty ( FilterValues ( Table::CheckboxField ; "apple" ) )
will, generally speaking, be a more robust method for checking to see if a particular value was selected.