Right--the CK 1 is a long-established, traditional, DC-polarized condenser capsule, while the CK 1X was an electret. So if you wanted discreet mounting, you gave up some sound quality.
That probably wouldn't be as much of a compromise today as it was then--the best electrets of recent years are excellent. But at the time no serious engineer would choose an electret if a "true" condenser was available.
Of course technically an electret is a kind of quasi-permanently polarized condenser, so in that sense they're as "true" as any other.
--best regards