Safe unique long numbers

I use Xojo Cloud and in order to create unique user’s identifiers when they register, i use
dim s as string = Format(Microseconds, “0”)

But I wonder if this is safer than define a reference date and then create this number based on today minus reference date difference in seconds.
Is there any opinion which is more safe? It is a question for mathematicians, maybe ?

GUID or UUID is considered better. There are functions floating around that do that and the MBS plugins have functions to do that as well.

Look at my M_String module.

You could also have a look at HashIDs
It is a hashing/de-hashing algorithm for numbers that generates unique strings.