This is a really excellent way to ease strained neck and shoulder muscles, by ensuring that your screen is at the right level - eye level. I am already feeling the benefit.
The riser is very roughly 50cm across the front and then approximately 30cm from the front to the "point" of the triangle at the back. This is therefore not an inconsiderate size and depending on the workstation you are using, this will either be too large, or inconsequential. On my desk, there is space behind where my monitor is anyway, so I do not "lose" any desk space by the triangular shape of the riser. If anything I gain some by the small shelf, but I agree with other reviewers that it is very delicate and wouldn't hold any real weight - but it is fine for discs or papers, which you want to keep to hand.
The pen holders are okay, but nothing special. They clip onto the central unit easily and are marked left and right to ensure that they are flush to the unit. I confess that I will continue to use my old desktop pen holder rather than transferring them across to the riser as pens aren't really held upright and they feel a bit lost, as if the space wasn't really designed for pens. It does give a nice symmetry to the design though, so I won't remove them.
I like the rubber feet for adjusting the height. The three levels are either 1) the basic unit 2) with one set of rubber feet or 3) with two sets of rubber feet. I have chosen to use one set of feet - 2 sets would have been too high and no feet was less stable as it was smooth plastic on the desktop. The rubber grips nicely and the unit is very stable.
The benefit I have felt on my neck and shoulders is definitely worth 5 stars, I just wish the pen holders had been more practical and the shelf a little sturdier, which is why I have dropped a star.