We're using the Syncfusion XlsIO in our trading system for external reporting (in excel) and for a lot of other internal document handling (special excel files) since 2009. In this year we have adapt the most of our modules to the new version 8. The benefit of using the XlsIO is that we're completly independend of the local installed excel version. We are handle complex excel sheets with a high amount of data. If we have problems the Syncfusion support needs mostly one or two days to identify and if it's required to fix issues. Requests for implementing new functionality are always welcome and mostly in the next or in the next but one major release available.