I want to make a accurate filter for my games.
The whole idea behind Roblox's new filter is to promote proactive versus reactive moderation practices to be as safe of an environment as possible. Allowing developers to implement their own filters doesn't guarantee as quick and efficient (?) of a system as community sift, with their COPPA compliant settings.
However, you can definitely add on to that filter, if need be. As long as you do use Roblox's filter, any and all of your other game-specific filtering needs should be acceptable.