i have used it althoug it's no longer on the car, but it was on for quite some time
the trick is to fold up the edges as in a real "tray" this will reinforce the otherwise floppy material... getting thin sheet, will have the added benefit these folds can be made by hand over a table edge.
one downside was it used to rattle when i slammed my door... making the car sound cheap... on the road it performed great and appart from dirt looked the same as when i put it on.
i have replaced in with a coroplast version now, basically cause i found a bigger sheet of that, but i'm thinking about reusing the original tray to extend the curent one, as it will be closer to the exhoust and engine (heat).