Saving your money is an important habit to get into. Being able to pull that money out on a rainy day? Also pretty darn essential. One of those two things might give you some trouble here, depending on how you feel about solving puzzles.
Rubik's Cubes, specifically. I don't know about you, but I've had some pretty spotty luck with them. And you're probably thinking what I was when I first saw this: "Oh, that's okay — I'll just leave it solved and never have trouble." Good plan, right? Well, it would be, except the piggy bank requires you to solve the yellow face of the cube if you want to put in money, and then solve the green side if you want to get any out. At least you don't have to sole the whole thing, I guess.
My mind's still being boggled imagining how well it works full of coins, to boot.
The Rubik's Cube piggy bank is sold in Japanese stores for around $40, though if you really want one you could go through, say, an importer.