> Spectacle used it's own keyboard shortcut recorder, while Rectangle uses MASShortcut [1], a well maintained open source library for shortcut recording in macOS apps. This cuts down dramatically on the number of bugs that were only in Spectacle because of the custom shortcut recorder.
FWIW, I use the Double Use Shift for parantheses. Tap left Shift for (, tap right Shift for ), and shift works as usual for normal typing and shortcuts. Karabiner is really an essential tool for me, especially this shortcut.
It looks like someone else is currently working on a Swift rewrite. https://github.com/rxhanson/Rectangle