When comparing SizeUp vs Divvy, the Slant community recommends Divvy for most people. In the question“What are the best power user tools for macOS?” Divvy is ranked 17th while SizeUp is ranked 57th. The most important reason people chose Divvy is:
Although it's not in the same level as something like bug.n, Divvy does support the use of keyboard shortcuts to move windows about. You can even create custom shortcuts.
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Pros
Pro Keyboard centric
SizeUp has user-configurable keyboard shortcuts for a set of pre-defined actions.
Pro Supports multiple monitors / spaces
Windows can be sent to different monitors and spaces. It can also be aligned as needed.
Pro Simple
SizeUp is easy and simple to use without having to configure.
Pro AppleScript support allows extending functionality
AppleScript permits adding features such as tiling all open windows. Additionally, FastScripts it allows the user to add keyboard shortcuts to AppleScripts.
Pro Menubar dropdown for shortcuts
Learning a bunch of keyboard shortcuts right off the bat may be difficult to remember at first, which is why a menubar shortcut for the app exists with all the shortcuts listed.
Pro Has keyboard shortcuts
Although it's not in the same level as something like bug.n, Divvy does support the use of keyboard shortcuts to move windows about. You can even create custom shortcuts.
Pro Requires virtually no configuration & is very easy to use
Divvy uses a drop and drag style UI that's simple to use and doesn't require any setup or configuration to get started.
Pro Reasonably configurable
You can change the grid dimensions and a very other visual settings to suit your needs.
Pro Super-fast access by defining your own hot key (mine Win+S)
Cons
Con Nag window
If a license is not purchased there is a nag window (which suspends function) that pops up when loading the app (at user login). The nag pop-up is also summoned at certain time intervals and by performing a certain number of commands (manually or by keyboard shortcut).
Con No on-the-fly split screen window settings
Unlike some other tiling window managers, SizeUp has no way to change the size of split screen actions on-the-fly. Any time a user wants to change how much room on the screen a window takes up when using the split screen function, they will need to manually change the settings, which can be time consuming.
Con Quite inconvenient to assign windows
You always have to use the mouse instead of having proper keyboard shortcuts.
Con No longer updated
While this may work for current machines, the last beta version (to be found on the site) is from January 2016.
Developer's twitter account has stopped being active as well, on November '16.
Con Windows 10 buggy
Not all keyboard shortcuts work. Support is non existent.
Con Installer requires admin rights, installs itself to AppData of the used account
Something to consider if would be used in a restricted environment.
Con Not free
Costs $14.