A skateboard is not a very efficient mode of transportation. It's about as fast as jogging. The boosted board is more like a bike...specifically, it's comparable to an electric bike, except that you trade off range to get greater portability (pretty useful to have in areas where bike theft is common).
Calling it a 'toy' is silly, and obviously intended just to be insulting. If someone buys a nice road bike to get to work, is that a 'toy'?
It's a yuppie toy. Sure yuppies need toys too, but let's not pretend this is something it's not.