The Master of Illusion downloads allow you to perform magic on your DSi to amuse yourself and friends, so if something like that amuses you, these might be worth checking out. Of the lot, however, Deep Psyche is pretty much the worst. Today's Special is novel, but it's really only briefly amusing and isn't really particularly interesting in the long term, though it's the only one you can perform by yourself. Deep Psyche itself isn't even that, as it's a one-note joke that wears out its welcome quickly and isn't worth showing off to anyone.
Vanishing Card might be worth showing to others, but it comes with all of the downloads, and you'd be better off with one of those tricks instead. All of these tricks come from the retail version of Master of Illusion, mind you, so if you own that, you don't need these, and if you're a fan of magic tricks, you might be better served buying that instead. Even for the low price, Deep Psyche isn't worth the investment, as it's simply going to be used, at most, two or three times before you never use it again.