I personally like dark themes, so the dark colors on the original immediately grabbed me, and the accent color is not one that I’ve seen often. The whole look (particularly of the lock screen) looks unique, clean, and stylish. Good choice of fonts, good layout. And definitely unique - everyone who saw it would know that it is not a common variant of iOS or Android, and that might invite them to ask and learn what it is. Now, the more GNOME-ish look will also clearly be distinct from iOS and Android, but it does not distinguish PureOS from Debian or Fedora or any other distro running GNOME. Obviously, people can change their GNOME theme, but having a nice, unique default I think would go a long way towards branding.
I tend to use the Adapta theme for GNOME, but if those original mockups ended up as a GNOME theme, I would switch in a heartbeat.