So… they charge half the price Apple does, and if you don't want to pay it you don't have to care because it's a standard m.2 so you can swap it with a retail drive (at which point you have both the original and the replacement for 50% more storage at a lower price), which you can't do with a soldered Apple drive.
https://imgur.com/a/ug87MaI
That 250$ more to upgrade to the 1tb from the 512gb.
the retail price of the upgrade is 450$