I think a point left out here is the fact that Apple is letting users upgrade after only paying half the cost for the phone. Other than Sprint, this isn't happening. With Verizon, you have to pay it off, no? With AT&T, it's closer to 60%. Yes, Sprint let's you upgrade, but that's because they are just trying to get people on their lousy network. If they ever start to have a good network and more people subscribing, they won't have such low options.
For people wanting to upgrade more often, who value Apple Care, and don't want to be tied down to one phone company (or any combination of the three), this upgrade program is surely the best deal.
"When considering the value of an unlocked iPhone Xs or iPhone Xs Max, bear in mind this important distinction: An unlocked iPhone designed to work on T-Mobile and AT&T’s GSM networks will not work on Sprint or Verizon Wireless CDMA networks. And to make it even more confusing, unlocked phones on Verizon or Sprint’s networks will work on AT&T and T-Mobile."
This is incorrect. There are only two models of the Xs sold in the US. A1920(iPhone Xs) and A1921 (iPhone Xs Max) as per: https/www.apple.com/iphone-xs/specs/. These phones will work on any carrier.