Functionally, the twin monitor arms work fine. I did find the small screws to secure the arms on assembly were a bit marginal - they were fine on one of the arms but they kept rounding when trying to tighten them on the other arm. The weight of the monitor is enough to hold the arms in, so no big deal.
I am using the desk mount clamp, attaching it to the back edge of my desk.... What really didn't work for me, however, was the fact that the upper and lower parts of arm are the same length, and therefore the VESA plates find their way back in the centre, right next to each other directly above the desk mount. In order to spread the arms outwards so two 23" monitors sit next to each (about 60cm between the VESA plate centres), I have to bend the turn the arms backwards away from the back edge of the desk. What this means is that I can't have my desk flush against the wall and the monitors are still way more 'in my face' than I'd like.