We have been happy to receive many queries about the sensor fusion algorithm. While it is based on Sebastian Madgwick's work and his original version can be downloaded from here, we have also made available our own slightly modified version (as required by the LGPL license).
Due to the number of queries, we have now moved from email support to direct downloads, i.e. we are now hosting the file on our web servers and you download it directly from here.
Nevertheless, we'd really like to hear about you, so don't hesitate to drop a line by email (info[at]finwe.fi) or by commenting here.