I've purchased almost all of the games this developer has put out, and my three and a half year old daughter loves them. However, the first thing I did on both my iPad and my iPod was turn OFF in app purchases so that my daughter (or myself) wouldn't be buying things without realizing it.
I think it's great that they offer the game for free so you can try it out before you buy it - I hate buying an app only to discover I really don't like it at all. I also like that it works on both the iPad and the iPod - I always have my iPod on me, so it comes in handy to help distract my daughter when we're at a restaurant or doctor's office. The game is a good value because the puzzles change each time you launch them - so it's not the same differences each time. I have recommended games from this developer to all of my friends who have small kids and an iPod/iPad. Keep up the good work :)