After evaluating similar tools from other vendors we decided to go for Syncfusion Xlsio. Our users performs their day to day task in excel and we have many requirements to develop .net apps which interacts with the excel , manipulates data in the spread sheet, this sheets have macros/formulas/cell references to other sheets,charts, etc. Syncfusion xlsio.calculate.base (which comes with the syncfusion back office api) comes very handy where you want to parse a formula which is a string value. We also use xlsio to save excel data in PDF files We are using this tool for few years and have no compliants so far. The support team does a good work on responding to your queries. I would higly recomed this to anyone who is looking to avoid installing office on their servers and work on excel applications.