As far as calculators go, you could do a lot worse! Adding a Mario skin on top of what would be considered by many to be quite an uninteresting subject sure helps me engage when I need to. Unfortunately, when I need to and when I can are too separate things, as using a DSi or 3DS during a school lesson probably isn't going to yield the best results.

Perhaps, if this was packaged as an actual dedicated physical calculator rather than a DSi application it'd be more acceptable to use when it's needed most but, for its low asking price back when this was available, you couldn't really go wrong. That being said, if you're looking for a more advanced calculator, you probably want to look elsewhere.