My take,
We had a tech out to do a house rewiring because all three Triple Play services were bad. He swapped my former Cisco 9865 for an Arris 3600, because when he was done rewiring, the Cisco was sluggish and some channels did not activate.
Well, the Arris would randomly reboot every 3-6 hours. Turned out to be defective, so I had another tech out to do an inspection. Everything was fine, except for the box, which he replaced with another Cisco 9865 and it is working great.
He said that he was only allowed to carry two six-tuner boxes in his truck at one time. The newest World Boxes from Spectrum are four-tuners. He also said that they don't give out new boxes, unless you are the first customer to get one because of turnaround expenses that would be associated with doing that. All boxes stay in the field through a give and take process until they die. Than each year, Spectrum gets new boxes and the process repeats itself.
The question for the OP is, do you watch a lot of shows were you need to record more than two things at once? If so, you can try to get a six-tuner box. BUT, if your two-tuner Cisco is working well and you have no issues, I would recommend keeping the two-tuner box. You never know what you are going to get in an exchange. Store and truck inventory changes daily from market to market and even from tech to tech. You could wind up exchanging a box with no problems, for a box with problems. Oh yes, Cisco is now Techicolor, but the names and software are the same.
Satch