Almost a 5!
Customer service: 5 
Overall: 4

(A 5th star will be added when/if they provide customer support in Portuguese language and also more options in Portugal, like direct debt).

I've been a client for almost two years now. For me the most interesting about N26, besides the charge-free operations, is the ease of interaction with their support. Security policy is also valuable. To change my phone number, for instance, I had to contact them and get a code that I had to confirm to a second operator who called up after the first contact. Sounds bureaucratic but I appreciate that when it comes to protecting my money.