Buy it with the prep. Why have rails in the bed when everything can be removed for a smooth bed with the factory set up. Later if you want to add the "pucks" or factory prep as it's called, you will be spending that much just to get it installed. If you want to install it later it's a real pita to go in and have to cut the holes in exactly the right places to line up nicely. I know this as I found a truck on the lot and added the puck kit myself. It wasn't the end of the world but the install sucked. They give a template in the kit and you have to cut 4 holes about 2 1/2 in diameter in your new truck bed. Now you have raw metal edges that have to be primed and painted. If you are ordering a truck I would absolutely get the factor prep. Jmo