Our extensions for Magento can be installed in every shop. It does not make any difference whether you start a new shop from scratch or if you have already a shop running.
We have been using this product for a long time with many of our clients now, but we recently ran into an issue where a new order made from the backend would not reverse charge VAT. I have had a lot of e-mail contact with Sven about this and he made time to fix our issue. Great extension, great support!