Think he has a series x, and the series s is replacing the second console.
It's all very easy, though, as described.
Only thing I didn't like is my series x kept auto updating games that required an internal install by copying (or so I thought) them from the external drive to internal. So I'd end up with copies of games in both places, delete the one from the console and a couple days later notice it was back on the internal storage.
Or so I thought, because it was actually downloading, not copying. Usually no more than 800gb bandwidth for a month, but first month with series x was nearly 5TB and had to remove games like haven and gears of war from my internal storage a dozen times before I figured out what was going on.
Eventually turned of auto updates, so not sure if fixed, but was pretty annoying.