Compare Keyboard Trays / Keyboard Drawers
Keyboard trays & drawers can be installed either with clamps, screws, or simply sit on your desk. No matter what method you use you need to make sure there will be enough room for the installation. Most keyboard trays have a 'track' that is screwed onto the bottom of the desk, although the basic models can clamp onto the desk and do not require tools.
Check that you have enough room to install the track underneath the desk as the track comes in different sizes, and that there are no supporting beams or ledges to get in the way. Some keyboard trays are designed for corner desks (more space available for the keyboard tray to move up and down away from the desk). Also remember to check your leg clearance as keyboard trays will lessen the amount of available leg room.
Most keyboard trays have an integrated mouse section, or even a separate adjustable mouse tray. Check that you will have enough room for your keyboard and to use the mouse at the same time. Also make sure they come with wrist rests for the keyboard and mouse, for when not typing or using the mouse.
The benefits of a keyboard tray are they have different adjustment options to suit the user and their applications. Some will have tilt adjustments, swivel, and some can be raised or lowered to a sit/stand configuration.
As they are essentially 'floating platforms', make sure that they do not bounce when typing, do not have any sharp edges where your hands go, and aren't height adjustable.