@marcus at synchromedia dot co dot uk
you misunderstood the comment. Of course you can use on and off, and they will work correctly.
But this entry is about *ini_get*. And if you ini_get() a value that is set to "off" in php.ini, you get returned 0 (as described above in the documentation). If you ini_get() a value that is set to "off" via .htaccess, you will be returned the string "off", which - if you use it in an if-clause, will be autoconverted to 1 (as is usual for strings).
So the problem is that which is returned by ini_get(), not what you can and cannot use in .htaccess. Sorry being unclear about this.