[tripplyons]

I think professional-grade is referring to their calculator not the statistic. I don't see what would make this site better than throwing your CSV into a spreadsheet or a simple script that would make it considered professional-grade.

[navquant]

One of the benefits is that the risk free rate is kept up to date on a daily basis. The calculation matches for each day the actual risk free rate, rather than just using the latest available value.