It all comes down to personal preference. Using the stick lets you keep your hands closer to the face buttons while using the touch screen doesn't. Any of the reviews saying the controls don't work or are extremely inaccurate never bothered to sit down and practice making the shapes for more than a minute.
i dunno, if the game defaults to using the touchscreen, but the stick is better, that's a knock against the original game design and the wii u for providing a useless feature.
still might get this at the Target buy two get one sale, but watching the Saur video just reinforces that there are control problems present, even if practice and discovery eliminate much of the frustration it's still weak that the touchscreen isn't effective when that's what's presented as the standard