Not that long ago I received one of those for my birthday. It’s the perfect gift for a geeky girl like me, it’s fun and playful and you can customize it. I think it would make an adorable engagement ring as well, especially if you don’t plan to spend a big amount of money (that you can save for your honeymoon for example, or nice gift for you grandma) on it. Rings are made by: Edition Mathea.
Where The Pretty Things Are 
Those are very cool! The one on the far right is my fav.