I have a Vitamix at home, but my parents have one of these Ninja blenders, and it's great. The Vitamix was several times the cost (even as a refurb), and might last my entire life, but the Ninja seems like a fantastic value to me. I like the stacked blades; smoothies get smooth in no time. Great upgrade from your Hamilton Beach or Osterizer.
Edit: it's actually easier to use, in my opinion, than the Vitamix. Sometimes you have to use the plunger to force stuff down to the bottom of the Vitamix. With the stacked blades on the Ninja, this doesn't seem to be an issue, at least with smoothies. Vitie is almost ten years old now and running strong with daily use, so durability has made it a worthwhile investment for us. But for $100, if you need a blender, get the ninja.