Anyone use a laptop tray?

[techs]

My laptop has some air vents on the underside so it is awkward to rest it on my lap and keep the vents free.
I have heard they sell trays that rest on your lap and have a hard flat surface for the laptop.
Anyone use any of these trays? Which one?

 

[eplebnista]

I use a large wooden cutting board. 14"x20" <--similar to that one