$6,300 is pretty inexpensive for a C-12 in good shape... I sold mine a few years ago for $8,500 each, but they were exceptionally good examples of the piece.
To answer your question... yes, they're that good... however, there are microphones that are being built now that are equally as good. They're not built in the PRC, they're not sold at your local Banjo Mart... but there are several mics that are as good, and in some applications even better.