A. Keyboard Size: Measure your keyboard to ensure it fits within the tray dimensions. Too big and it may overhang, too small and there may be an inappropriate amount of room for the keyboard to slide around.
B. Mousing Surface: If you are going to use your mouse on a pad next to your keyboard, make sure there is adequate room for the mouse pad to rest on the platform on the side that is most comfortable for you.
C. Wrist Rest: If you are using a keyboard with a built-in wrist rest, or have removable wrist-rests for either keyboard or mouse, make sure you allow for the space that these will take up on the platform when selecting a keyboard manager.
Height: Keyboard trays are traditionally available in fixed height adjustments or in an infinite range.
Tilt: Keyboard trays can tilt for custom comfort when typing.
Sit/Stand: Longer arm allows for the keyboard tray to be adjusted above the desk surface for standing or sitting use.
Swivel: Allows for the keyboard tray to rotate maximizing user comfort.