iRobot Roomba 560 Robotic Vacuum

I have owned 2 roomba schedulers, each lasted slightly over 11/2 years. the brushes stopped working and they started making a very loud grinding noise. We used them every day ( and cleaned them everyday) on our hardwood floors, we do not have any carpeting/rugs. Let me tell you also that we no longer have any kids, but have 9 cats. Our second unit just died and after much deliberation decided to purchase the 550, a unit that seems to be the same as the 560/570, but is sold thru Costco. Paid $279.00. Just got it out and it is absolutely wonderful. It is about 1/2 the noise of our prior units and seems to clean much better, the slight slowdown prior to touching a wall is very cool, since we had already had our house roombatized ( no carpets, cords, etc...) the non tangle option i'm unable to evaluate. Irobot does need to extend their warranty, but the ability to replace parts seems real cool.