When comparing Karabiner vs Transmit 4, the Slant community recommends Transmit 4 for most people. In the question“What are the best power user tools for macOS?” Transmit 4 is ranked 4th while Karabiner is ranked 29th. The most important reason people chose Transmit 4 is:
Exchange data with FTP, SFTP or WebDAV servers or your Amazon S3 storage.
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Pros
Pro Low-level key bindings/mappings
For example: Fn+C now calls up contextual menus for me with:
<!-- Fn + C = same as right-click mouse -->
<item>
<name>kybd control click</name>
<identifier>private.keybd_to_control_click</identifier>
<autogen>
__KeyToKey__
KeyCode::C, ModifierFlag::FN,
KeyCode::VK_MOUSEKEY_BUTTON_RIGHT
</autogen>
</item>
Pro Make FN key into a new modifier key for custom shortcuts across apps
Pro Fast and powerful file exchange client
Exchange data with FTP, SFTP or WebDAV servers or your Amazon S3 storage.
Pro Supports Amazon S3 & WebDAV
In addition to FTP, allows exchanging data with SFTP or WebDAV servers or your Amazon S3 storage.
Pro Enable a server connection as a normal disk in your Finder
So you can access your storage without the Transmit client.
Pro FTP Sync
Scans local and remote for difference and only transfer modified files. It's not rsync, but it's the next best thing
Pro Can enable a server connection as a normal disk in your Finder
So you can access your storage without the Transmit client.
Cons
Con Difficult to configure custom actions
Configuring custom actions requires editing an XML file with very strange syntax, for which it's difficult to find good documentation.