I don't see what everyone has against the new add-on. I mean, be happy it's not a new system (there have been rumours about releasing a 3DS with 2 sticks), it may be bulky, but it looks ergonomic and even though it looks huge in pictures, if you get your 3DS and pretend it's attached then it isn't too big. Also it adds some new shoulder buttons. As said before, it is being made for Monster Hunter tri G, so you don't HAVE to buy it... I personally think it doesn't look too big and even if you do take it out and about, you normally have two pockets, don't you? One for the console and one for the extra. Or you can put it in your bag. Simples.
EDIT: Apparently, it's only an extra 3cm on the 3DS, so that only makes it around 16cm alltogether. The PSVita is 18.5cm. Not that bulky if you ask me.