• As the column will hold only English language letters and digits, we don't need the additional bytes required by the national character data types

    Not quite correct. You don't need to use Unicode data types for non-English letters. For example, if the identifiers contain English letters, Russian letters, and digits, you can use Cyrillic collation:

    CREATE TABLE #tmp (id CHAR(10) COLLATE Cyrillic_General_CS_AS)

    INSERT #tmp VALUES ('??????1') -- Russian word for 'hello'

    INSERT #tmp VALUES ('Hello2')

    SELECT * FROM #tmp

    The result of this query is in the attached picture.

    If you need to operate with more than one national alphabet, using of nchar/nvarchar is the only option. Otherwise (only English alphabet, English alphabet + one national alphabet), any of char/varchar/nchar/nvarchar data types can be used.