Kiwi is nothing besides a stand-alone browser set to google.com/mail as the homepage. With the exception of the menubar and color coded accounts, there are literally no additional features of this app from stand-alone browser-based gmail. Even the lauded "send huge attachments" is simply using gmails browser-based google drive integration. Its no faster than the browser-based Gmail and they require you to pay for standard gmail features (multiple accounts, keyboard shortcuts, etc). A little bit over-promising to take all of Gmails features (hangouts, etc) and advertise them as features of your app.
There are two free tools that do this, but much more universally (i.e. for any web app, not just gmail) - and without needing to pay for "extra" features. Check out Epichrome or Fluid App for free alternatives.
timshutes about Kiwi for Gmail Lite, v1.8.93