The BK-9 is essentially a "leaner, meaner" Brute.
The Brute was designed a decade ago out of inferior steel for the job which is one reason why it is so beefy and too brutish for some.
It is a stout muther, but the sabre grind and thick stock= thick edge.
Which translates into inferior performance in most cutting tasks to the CB-9.
The Brute is a neat knife but too bulky for many and some find the recurve hard to sharpen.
It boils down to personal preference. If you want a beefier knife go with the brute. If you are looking for more of a real world big utility chopper go with the CB-9. FWIW, I think the BK-9 sheath is s uperior unit in many ways to the Sheath of the Brute.