Uniqueness should not be the primary consideration for a clus key. Uniqueness should be a factor, but it's not the most important factor. The proper clus key depends still depends more on how the table is used.

For example, for a typical log table, there will be a datetime logged. It is not unique, since several INSERTs can easily occur within the 3 ms between datetime intervals.

Lookup is 100% by datetime for typical log uses: what happened with <x> activity between 11:30AM and 12:30PM yesterday.

Also, say you've chosen to add an identity column to the table; by definition, that column will be unique (whether constrained as such or not, under careful use).

Even so, the clus key should be the non-unique datetime, not the unique identity.