It's well-designed, though not perfect. They've really gone for simplicity and, indeed, it is mostly easy to use. Setting it up was seamless, though not entirely intuitive (I had to follow the instructions a bit). The app is very nice and simple to use (my mother-in-law was able to set it up without any help, which is quite something). It's completely safe too, because contacts must be approved by me before they can be added to his toy.
The main drawback is that it's almost *too* simple. For instance, for the sake of simplicity, they've kept the number of buttons to a minimum. Tapping a button will do one thing, while press-and-holding that same button will do something different. I think it'd be easier for kids to actually have a couple of extra buttons rather than make buttons do double-duty. That being said, with a little guidance, most kids will probably find it pretty easy to use.