I know it says up to 24" but is there any reason it couldn't work with a 27"? Are the mounting holes further apart or something. Ah I guess the monitors wouldn't fit?
The arms might not be quite long enough to fit 2x27" monitors unless they were angled away from the centre (rather than towards the centre like you would want)
If the bezel was really thin on the monitors you might *just* get away with it to be fair, but I'd not want to recommend it as I don't know for sure!
The back of the monitors should have standard 100mm x 100mm VESA mounts - you screw in the mounting bracket to the monitors, then you position the bracket into the mounting arm itself at any point along the arm you want.
I'll take a pic of the rear of the setup for you this eve.