I have a friend with Nova Drift on GOG and he didn't get the Glistering Update that is instead present on Steam.

I wanted to buy it here on GOG during these Christmas sales, but should I buy it on Steam instead?

Just bought it and can confirm that the version of the game on GOG (as of the date of me writing this) includes the Glistering Update. From what I've found when searching around for info, the updates seem to release a day or so later than Steam here on GOG.
Hope this helps anyone considering buying the game here on GOG.