Negatives of the crenelated bezel TurboHead used by the M6-CB compared to the scalloped (M6) or old style no rim effect M6 are as I see them:
Extra length - may not fit in pouches or holsters etc.
Style may be considered too aggressive for some situations - it may be considered a 'weapon' either by the 'social' groups or 'authorities' prevalent in some environments.
The M6-CB could be more difficult to carry comfortably in your pocket and it may get caught or snagged when an attempt is made to deploy it.
Personally, I don't care for the -CB versions of the M3 and Millennium TurboHead. I do not need them, nor do I find them useful.
Al