I'm a long-time user of free/open source software, and write various things for both fun and profit. I don't take myself all that seriously and I do all of my own stunts.
You can find me at these fine establishments on the web: Open Source Musings, The Monday Kickoff, Weekly Musings. and The Plain Text Project.
Authored Comments
I can't give you a feature-by-feature comparison -- it's been a while since I've used Sheets (I de-Googlized my life some time ago). And there are any number of spreadsheet features and functions that I don't use, have never used, and probably will never use.
What areas/functions of Sheets and EtherCalc do you want to compare?
Well, it's up to you to decide what information you put into an EtherCalc. If you're using a public instance, then I'd advise against including information like bank or investment account numbers. I'd hope people would have enough sense to realize that.