Review on Versatile Projector Tripod Tray: Secure & Mountable Platform Holder for Projectors, SLR Cameras, Laptops, DJ Equipment, Mixers, Amplifiers, Audio/Video Devices (Tray Only) by Matthew Augustin

I think it is a good item that will serve its purpose well. I see some complaints that it's just cheap metal, it's a shelf, you attach it to a tripod and you can put things on it. It's not 3 inches thick and doesn't weigh 40 pounds, of course it's flimsy metal, but just make sure your tripod can handle the weight and you'll be fine. I'd be more worried about the tripod than that this shelf won't support the weight. Most tripods are only rated for a few pounds if you don't have a good one. So make sure your tripod can bear the weight when you put something heavy on it. If you're putting a large amount of weight on it, just make sure your tripod is up to the task at hand.