When comparing Spectacle vs Backblaze, the Slant community recommends Backblaze for most people. In the question“What are the best power user tools for macOS?” Backblaze is ranked 10th while Spectacle is ranked 35th. The most important reason people chose Backblaze is:
The default configuration includes everything except for system files to be backed up. That also includes external USB drives. This will work for most people. It can, of course, be customized to each person's liking.
Specs
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Pros
Pro Free and open source
Spectacle is licensed under MIT with source code available on GitHub.
Pro Simple hotkeys
Spectacle offers easy-to-remember preset hotkeys.
Pro Mouseless
All windows in Spectacle can be controlled with keyboard shortcuts, so no mouse is needed. This makes for a fast way to control windows.
Pro Great UX
Spectacle is easy to use and configure. It's plug and play.
Pro Low footprint
Spectacle only uses up 18-19 MB of RAM, which means there is not much overhead by using this app.
Pro Multi-monitor support
Pro 7+ years of use
Using it for 7 years
Pro Beginner-friendly defaults
The default configuration includes everything except for system files to be backed up. That also includes external USB drives. This will work for most people. It can, of course, be customized to each person's liking.
Pro No file size or traffic restrictions
There are no limitations of file size or amount of data you can upload. The $5/mo plan gets you unlimited cloud storage.
Pro Excellent restoration performance
Backblaze creates a zip file of all your files for you to download, thus decreasing the amount of data you need to download and increasing the speed of the download since it's one connection instead of multiple that need to be opened and closed for a list of files.
Pro Secure
AES encrypted files are transferred over a secure SSL connection.
Pro Download any backed-up files from any web browser
Some backup services like Carbonite require a client to be installed to restore files. Backblaze allows you to login and download any or all files from a web browser, meaning it also serves as an ad-hoc cloud storage platform.
Pro Users can order a physical copy of their data
You can have a flash drive or an external hard drive delivered to you. They cost $99 and $189 respectively.
Cons
Con Not maintained
The software is free, but no longer seems to be maintained.
Con Impossible to add new functions
While keyboard shortcuts can be changed for the available actions, there is no way to add custom actions which in turn limits the functionality of the app.
Con Limited window sizing capabilities
You can use 1/2 of the screen vertically and horizontally (divide into 4 parts). You can also use the screen in thirds too, but only the left and right third: you can't use the 1/3 in the center. There is no way to do a more granular distribution.
Con Breaks on macOS High Sierra / Chrome or Firefox
Doesn't support side by side windows.
Con Doesn't work with any Adobe products
There are some apps like Adobe Reader that do not work with Spectacle. Basically, any app with a heavily customized UI that breaks OS X accessibility will not work correctly under Spectacle.
Con No Linux support
There's no Linux client for Backblaze.
Con Pay extra to keep deleted files permanently
Additional $2/Month plus $0.005/GB/Month for files updated, changed, or deleted more than one year ago.
Con Backblaze does not support network (NAS) drives
If you use a thing like Drobo, Backblaze will not back it up.