I'm not sure which Ninja we have, but I found the deal at Kohls to awesome to pass up. They had the one we have (it has 4 special cups for making smoothies and they pop right in the dish washer and have lids making them drinks on the go) and it was 30% off; I had a coupon for 30% off and that made it a no brainer.
My family uses it almost daily year round for smoothies; they do taper off in the winter here, because it just gets too cold here. I like that the unit isn't huge and goes right into the dish washer. In my dreams, a super Vitamix would be amazing, but I'd need to use it all the time or I'd feel guilty spending that much.