This is one (of the many) new toys Kitsune got on Christmas. It's a Kyjen Tennis Ball Slider puzzle, and retails for about $15 on Amazon. Kitsune is, as most Papillons are, a really really smart dog. I've thought about getting him puzzle toys before, but this is the first one we've ever tried with him.
The toy is made of plastic, and comes with two tennis balls. You can watch the video I posted to see how it works. Basically, your dog has to open the two side doors (that can contain tennis balls) before he/she will be able to slide open the middle compartment, which covers 4 indented sections where you can hide treats.
I didn't think it would take Kitsune long to figure out how to work this toy, and I was right. He figured out the puzzle very quickly, but still has a lot of fun with it. Even though he knows how to open it really well now, it still usually takes him some time to maneuver open all the sections of the puzzle. He really seems to enjoy working to get the puzzle doors all open. And oftentimes, even when I don't put any food inside the toy, he'll spend time playing with it just to get the tennis balls out, or to double (or triple!) check that he didn't leave any treats hiding inside.
Overall I'd recommend this toy. It doesn't seem like it'd be too hard to figure out, even for a dog who might not be so gifted in the brains department. But smart dogs, especially smart dogs who also love tennis balls, can have fun with it too!