(bias alert: I'm part of the team)
It's not free, but IMO it's the most Excel-like Web-based spreadsheet money can buy. You get support for Excel syntax and formulas, hundreds of Excel functions, XLSX import/export, print-to-PDF, virtual scrolling, OS clipboard integration, etc. — and it all runs in the browser.
If I tried and found myself liking kendo-ui, I'd probably end up even more frustrated from not being able to use it for personal projects.
EDIT: Just wanna add that you guys have done great work. Poking around the component demos is really slick.
Second - we use react and kendo had started exploring react only in oct2016 (we have our react HOT app in production since Nov 2015). I'm Not sure what's the status since googling for a react kendo spreadsheet component does not get me much.
But I would switch If you had a clean pricing for the spreadsheet, clearly showed by comparison where it was superior..And most importantly, react.