I'd say you run the risk of losing customer faith in moderating your own thread as if you take the same approach to Dapol has in the past and effectively censor negative posts and shut down legitimate debate (such as the Companies House strike off threat and subsequent issue around outstanding accounts submission). This would be bad for DJM.
Leaving debate on an established and independent Forum such as RMWeb means you don't have to devote time to moderating, you have independent (and fair) moderators looking after threads and posts and will reach a wider audience than just those who are your disciples and detractors. Not everyone will know who or what DJ Models are so are unlikely to join a manufacturer specific forum, however, through BRM, many more will know of and be likely to contribute on RMweb.