When comparing Magnet 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 Magnet is ranked 51st. 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
Easy to learn keyboard shortcuts.
Pro Intuitive handling
Just drag the window to one of the sides of the screen and it snaps there. This is especially useful for those who can't be bothered remembering the shortcuts.
Pro Cheap
At $0.99, it is not that expensive.
Pro Mouse controllable
Supports dragging a window along the edges of the screen to activate.
Pro Do not have to learn or remember keyboard shortcuts
Pro It's often on sale
For example, at the writing of this pro it's currently at $1.
Pro Up to six external displays supported
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 Cannot setup custom sizes and window positions
Unfortunately, you can only move windows to preset positions.
Con Can only be purchased from the App Store
Magnet is only available in App Store.
Con Can't hide the menu bar icon
It would've been nice to be able to hide the icon so it doesn't clutter the menu bar.
Con Interference when switching between folders
Default Folder-X app "warns" that Magnet App may interfere with it's ability to switch between folders in Open and Save dialogue boxes.
Con Causes cursor bugs in IntelliJ IDEs
Unfortunately, Magnet causes the caret to bounce around in IntelliJ IDEs, this is very annoying.
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Con No longer updated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.