You never want to use one of the trays sold for your car seat. Think of it, do you really want something that hard strapped to your child ina crash... it will go right into her abdomen and face. Not a good idea. plus it will void the warranty of your car seat because you cannot use aftermarket products on a car seat.
We used the Side Riders on our car seat. They are mesh and pop open adn clip to the side of the car seat on the fabric. Still not the absolute best solution since its still an aftermarket product, but its not right in front of your child and its not as dangerous. You can pick up a pack of two for $10.