The Macro VBA will integrate programming codes into the Excel file. If you have 30 xls(x) files, that code will repeat 30 times, which makes it difficult to control and upgrade.
The Mycel add-in will integrate programming codes into Microsoft Excel software, not into the file. This means if you have 30 excel files, the files will only contain the final result, not any control code. Thus, when the functions are upgraded, all files can be updated instantly.