These are cheap obviously, but they are not fit for purpose. Obviously, they are hard to attach without leaving bubbles - which is why they come in a pack of 6. That could be down to user error though.
The big issue is that although they do the protecting task fine, they immediately scratch very noticeably. If i wanted my phone to look scratched, i wouldn't put a screen protector on it! And when i say immediately, i mean a large scratch appeared as a result of me swiping the screen with my finger immediately after the protector was put on.
By comparison, i bought a similar sounding (and similarly cheap) product for my HTC Sensation XE screen almost 3 years ago, and have only used 2 of them in that time (look for my review of that product). And those ones don't show the scratches. So these Nokia Lumia ones are below the industry norm.