If I buy 1 voucher now worth 15 euro and then redeem at Netflix I will have 1 month Netflix and then nothing? I don't have a credit card etc and want to use trm Netflix
Yes, then you can't watch Netflix until you pay the amount again.
There's always a trial month at Netflix. Then you can add another one with your 15 euro. But then you have to quit otherwise it will continue.
First of all, they always have a trial month and the price for a device is just around 8 euro.