I actually have built and used both each for about a year and the HeavyDuty cargo tray is a WAY better solution than the drawer. Even the single large drawer system that I build (best way to build a drawer IMO). The factory cargo tray and the steel tray that I built dont even compare (Strength, tie downs, perfectly level with folded seats, etc)
The biggest advantage is being able to take everything out and have a fully flat floor, I now pack all of my gear in boxes and I can tailor my load out to the activity. If I am going to a park or somewhere not involving serious off-roading, I can bring just my camp and kitchen gear. Furthermore, for solo trips, I can ditch the RTT for some improved MPGs and move all my gear to one side of the truck and sleep in the back.
Anyways, here are pictures of both.