Interestingly, vQmod was originally developed for Open Cart ! But due to "openess" of the design, it has been used by other systems too.
In OpenCart (OC), extending your site's features usually results in modifying the program core codes. There are many reasons why this practise in not favorable - a major one is that it is not easily reversible. Say when you modified some codes and wanted to reinstate the original for some reason, it can be quite tedious.
