I'm not sure any complicated autonomous device operating in a dusty environment is going to run without any issues for 5 - 6 years. If you read the threads for the main robovac brands, they all seem to attract posts from owners who've had something fail, fall off, wear out or not work as they'd expected, no matter if they're Neato, Roomba, LG or Samsung.
Judging from forum posts, Roombas have a reputation for poor after-sales service and costly parts. They also need de-hairing after every run even without a pet and the lighthouses constantly need new batteries. Since you have 3 robovacs already, you're no doubt aware of the abilities of each model. While Neatos are clever, fully automated, powerful and efficient, they have gained a reputation for being unreliable thanks to 3 main issues that have hopefully been resolved (wheel spring, RPS and most recently, faulty batteries), however, Neato has earned a reputation for excellent after-sales service and quick replacement, a week or less if you're in the US.
Since you already have 3 different models, maybe just watch and wait, especially since you've yet to buy the new home. The Mint does scrub, something the others can't do, so maybe keep it for the the kitchen and bathrooms? Personally though, I'd return the Roomba since you hardly need two robovacs and a scrubber for one apartment. Once you buy a bigger house, then consider another one if you don't want to carry the old one up and down stairs. There may be an improved model by then too. Ending up with a Mint plus two Neatos and two chargers should cover a 3000 sq.ft two storey home quite well. Even if one Neato needed repair, if the remaining one can use the other charger, then there's hardly any interruption to the cleaning routine while it's away for a few days.
Neato XV-11 SW 2.0 Board Rev 113 / 3500mAh battery pack installed May 2013 / Pet & Allergy pack installed Sept 2013