Had my NutriBullet Prime for a couple of months. Two of the 32 oz cups are now broken because they get jammed in the unit and cannot be removed without breaking off the locking tabs. The rotation of the motor loosens the blade attachment and the separation of the cup from the blade locks the whole thing together and cannot be twisted to turn it off. The unit remains running until unplugged because the tabs are pressing the on-off switch. The cup is now wedged in the unit and must be broken to get it out. We assumed that the blade was not tight enough, but even when we tighten it as much as we can, it happened the second time. Now we can only use it by pressing down on the unit, but not locking the cup to the base. Clearly this is a major design flaw.
I've been using the 600 watt model for years and a friend mentioned that the 900 makes a much smoother smoothie than the 600 so I upgraded. I can say that it definitely does and I recommend it especially if you use a lot of kale, parsley, ginger, etc.