I've been using Syncfusion Essential XlsIO for over 7 years now. I recently started a new project and needed to be able to import data from differently formatted Excel documents. XlsIO has a great method to return the contents of an Excel sheet as a DataTable. I ended up having a problem opening up a .xlsx version of an Excel spreadsheet. I posted my problem to Syncfusion support and within hours Sridhar replied back with a simple solution for me. I have nothing but good to say for Syncfusion and their product Essential XlsIO. We also use their GridGrouping control and are very happy with it.