My wife has one and loves it. Personally I don't really see the point but it is fantastic for those that don;t like to cook, know how top cook, or are too pressured for time.
As with most things the quality of the food will depend on ingredients and the recipe. You get those sorted and you can generate world class food. In particular my wife makes fantastic curries from scratch, first heating the whole spices before grinding them etc.
On the cost side a decent food processor is not far of that. Our Kitchen Aid is about 400 quid for example, our spice grinder nearly 50. You then have a cooker with high precision temperature control.
The downsides for me are that you don;t really fry anything, e.g. chopped onions slowly saute but due to the shape get steamed a little.