I have the virtical Tonneau, which I got from Nissan for about 95 quid. I don't have a horizontal one, despite being a GT. You can see into the back part of the boot with the hatch closed. Also anything white (e.g. shopping bags - yes it does get to go to Tesco) reflects onto the back window. Not the view I want when I look in the rear view mirror. So if there is something I can get to sort this out, I want it.
The one that fills in the gap between the back of the window and the strut brace, attaches to the tailgate and comes as standard, but you can get a replacement IIRC they are about £50