Authentication If you use the recommended platform, Google Drive, your data can be protected by 2 factor authentication if you desire that.
With 2 Factor Authentication, for any login on a new device (laptop, desktop, mobile device, etc), you will enter your password and prior to gaining access to your data, you will be sent a confirmation code to your phone that helps verify you are you. It doesn't get much better than that.
Google has a keyfob type system for secondary authentication, but not sure if/when that will ever be a public option.
Distributed Data No matter if you use Google Drive or Excel, your accounting data is NOT in the same database as that of millions of others. It is the aggregation of data in a single repository that makes for big prizes for nefarious interests. If the data is distributed in private bins, as this would be, there is no target for nefarious interests to shoot for and this is a big win for all consumers.
O2) File Sharing and File Syncing
If you use the recommended platform, Google Drive, your options for file sharing are numerous and there is no need for file syncing as your file resides in the cloud at all times and you are always accessing it there, so no "syncing" is required. What you see on every computer is identical all the time, and in fact you can watch collaborators work in real time if you'd like.
This is truly paradigm shifting technology that is finally finding it's user base.
And more... In addition to just sharing the file, there are ways to manually and automatically email collaborators from inside the file. There are also ways to publish parts or all of a document online as a webpage for viewing purposes. The options for sharing can't hardly get any greater.
O3) Graphics Customization
Want to add your own logo anywhere? Go ahead. From top menu it's "Insert>Image". Want to add images for some reason? Sure, anywhere you'd like. Same instructions. Want to change around all the colors we've chosen? Sky's the limit.
This is just a spreadsheet and you are only limited graphically by the limitations of a spreadsheet.