Count unique values in a column for each row that meets 3 criteria

slightly shorter ARRAY formula:

=SUM(IF(FREQUENCY(IF(($B$10:$B$19>=$B$5)*($B$10:$B$19<=$B$6)*($C$10:$C$19>=$C$5)*($C$10:$C$19<=$C$6)*($E$10:$E$19<>""),$E$10:$E$19),$E$10:$E$19),1))

or

=COUNT(1/FREQUENCY(IF(($B$10:$B$19>=$B$5)*($B$10:$B$19<=$B$6)*($C$10:$C$19>=$C$5)*($C$10:$C$19<=$C$6)*($E$10:$E$19<>""),$E$10:$E$19),$E$10:$E$19))