Why are you trying to encrypt online spreadsheets? It's very unlikely that you're going to get much operational security out of the encryption features in a spreadsheet application; you will get far more security out of careful use of sharing and authorization controls, which are things you can get from Google Docs and not so much from other platforms.

Remember too, if the tool you're looking at works entirely in a browser, without an extension (sometimes even with an extension!), it's not "end-to-end encrypted"; it's as encrypted as the server wants you to be as you run it.