Playing with your food

My dog eats her dinner so fast it is literally over in seconds. I would really like to use one of these clever devices to change her food into more of a longer lasting game.
Which is the best brand for using in something like a Maze or a Buster Cube?
Has anyone already tried a few varieties out?
Is it better to have small round shaped kibbles that roll?
Do share your experiences!
Gill Knight, London