This unit is easily assembled, and made from plastic. It is attached by a sticky foam pad onto the side of your monitor - this is my only concern about this product, as it would be so much better if it had a clip of some sort rather than sticky foam; I haven't tried removing mine from the monitor yet, in case I can't put it back on.
It makes it a lot easier to look at the screen as well as the paper - rather than having to look down at the paper on the desktop, as it is in the same eyeline with your monitor. There is a clear transparent sliding 'ruler' on the front of it, which underlines which bit of text you're working on.
We have been using these at work for about two years now, and they are a good work aid - they keep the desk tidier, too. The Health and Safety Nazi insisted upon us using them, claiming that it was good for our backs. I don't really follow that argument, but this device proved more useful than I'd have credited it for. It gives a good impression to the boss, too!