The most common comment that I hear about Humanscale keyboard trays is "I've heard about the Humanscale 900 and 500 keyboard trays, but I don't know how to decide between the two."
The main difference between these models is that the 900 keyboard tray is 19 inches wide, and it can have a number of adjustable mouse platforms added to either the left or right side of the board, while the 500 keyboard tray is 22 inches wide, which is wide enough to accommodate a keyboard and mouse on the same surface. Which one you'll choose is just a matter of personal preference, and it seems to be fairly equally split in our office.
I prefer the 500 board, because I like having the mouse on the same level as my keyboard, and it makes it easy to switch between a right-handed and a left-handed mouse. Other people here like the adjustability of the high clip mouse platform on the 900 board, which can slide forward and back along a track on the side of the keyboard platform, giving it height, depth, swivel and tilt adjustment.
Either board can be mounted on any available Humanscale track (sizes range from 11 to 27 inches, with 22 inches being the standard track length on both), and both are compatible with the newest 6G mechanism, which offers a height range of 1.75 inches above the track to 5.25 inches below the track.
See all of our ergonomic keyboard trays at TheHumanSolution.com.