Transparency and Immediacy
No hidden charges, quick and simple ways to pay people and receive money, great financial products you can add on and manage 24/7, and everything is right there in front of you and super simple to use. Another very simple but deceptively powerful feature is just the immediacy of the app and how it shows the incomings and outgoings of your finances right there, right now. 

Seeing and being notified immediately of what you've paid for and what you've received (including the recurring (automated) bill payments) meant I immediately got a hold of my finances and could control them. I was then able to stop using a credit card with another bank and quickly began saving. I have N26 to thank for that.