Company itself is great. No issues with car rental.
Service was friendly.
Only qualm was getting to this place.
57 NOK by local bus (as at June 2019) - number 1 (available near the train station, or anywhere along the mainroad if you caught a bus into Narvik), you can show the bus driver where you're going, or you can use GPS google maps to track, as soon as you hit Ankenesveien then you get off at the top of the ramp. The bus stop to get back when you return the car is opposite to where you get off.
The Sixt is located inside the car dealership/repair centre just below in the industrial area - many cars are parked outside.
There are no signs for Sixt until you get up to the door - you may see a few cars have plate borders with Sixt Bilutleie but thats about it.
Buses also run infrequently, so best check the timetable.