I've been to the one at Sandown Park, yes there are some free stuff to be had. Last year giving away those mp3 player/ data keys with the 17th changes on. Did spy a few lunch boxes from MK as well.
If you go to this one leave your coat in the van/car, it was so warm inside it felt like you were melting.
Yes i've been to them, they are good, they are helpful, its a good way of introduction ot new products, last time i went (Sandown park) i got some freebies too.