Wunderlist on Linux doesnt claim to be anything more than a wrapper around the official Wunderlist web app (which, yes, you could just open in a new browser tab).
Some people like their web apps to be moreapp-y. Electron, especially when developers leverage the native system integration it offers, is a great framework for doing creating desktop apps that act like, well, desktop apps!
Versions Wunderlist for Linux
ver: 0.0.8 : May 22.2018
Screenshots Wunderlist for Linux