I have been using Syncfusion XlsIO for just over 3 years and am very happy with its performance, scalability and sheer number of features. I used to use Excel.Application via com-interop in .Net and suffered many issues over time so I needed a solution that would give me better reliability and ideally better performance. XlsIO delivered! The documentation is very good and the software gets regular updates throughout the year. From time to time I have a need to contact product support to either report an issue or ask a 'how-to' question. I find the web-based support easy to use and the response time is pretty good. I have sometimes been given patches to fix an issue without having to wait for the next release which I appreciate.