BFD2 is complicated that is what makes such a great drum VST. There are ways to use in a less complicated way by using presets but that is useful if you only want a very quick usable sound. I don't believe BFD2 is for everyone. I think it is great for very advanced users that are looking for a versatile great sounding drum synth. Session Drummer 3 is ideal for quick use. Its good for those that are just getting started too amd can be used by all users with good results. But BFD2 is completely customizable as far as the sound you get. But it takes a little bit of work.
As to the mixer to me its rather simple and not unlike most other mixers on other drum synths except what you route and where can have a big impact on the sound you get.
Unlike other mixers its not just directing drum to a track but how the mics for example get routed too. With that kind of versatility comes complications.
Think about this the manual is a full 200 pages long.
BTW did tell you guys its a great drum vst?