This is really very good value for a few quid. Relatively modern cancellations like this were not popularly collected. As a result, they are difficult to obtain, especially with commercially used examples.
C1 refers to the size of the circle as well as the letters. He gave an EDS of 28OKT72 but this first day cover has the date of 1FEB71. Probably not in use for many years, but at least we know it was in existence between these two dates.
It came with a booklet describing the subjects involved in the stamps which is an added bonus. You can see a more current version of the KK Airport cancellation in my post in July 2012 by clicking on this link.