It's pretty cool but it is SO HARD to do the magnet thing!! You have to hold the magnet riiight over the nail, and keep it totally still for 30 seconds or so. The biggest problem I found was that the polish draws itself upwards to the magnet and sticks to it like some lame cousin of the T1000 from Terminator 2.
All in all, it's a nice novelty, but it's very hard to do well, and even when you do do it well, it's too subtle to really wow anyone, so what's the point in all that effort