Mine has a treat ball, this one:
here
Think mine was from Amazon. Cat half-heartedly rolls it around depending on his mood. More often than not he gets bored after a minute or two and pesters me relentlessly until I roll it about for him/ get bored of the whole charade and open it up. I also get the glare of disapproval!
You can set it to different sized openings but there are only two worthwhile ones - slightly too big and slightly too small, i.e. too easy or too difficult 
Probably depends how determined/ greedy your cat is. Definitely worth a couple of pounds to see how much of a problem solver your cat is before investing in anything more expensive.