Do not use Kiwi Browser. It’s based on an extremely out of date version of chromium and therefore very vulnerable.

There are far more robust methods of fingerprinting to spy on users anyway (adding up all the details of screen size, available fonts, language, os, etc, etc), so I don’t think removing the user agent would have much impact in reducing fingerprinting alone. It’s also useful as a quick and simple way to check the type of device, os, or browser the user is on and serve the correct content (download link for one’s OS) or block troublesome clients (broken bots)