New birds tend to be shy about eating but they really will eat if they're hungry. Make sure you offer a variety of veggies and such to your keet - seed is a good start, but it's not a full nutritious diet
I don't know that any seed is really "better" than any other in a global sense, it would sort of be like arguing over types of bread. They are all just various breads in the end. I suppose I'd choose a seed mix that had a variety of shapes just for interest's sake, but it's more important that you have the veggies and other things vs choosing a particular brand of seed.