Think of filtration in three parts: mechanical, biological, and chemical
I just use mechanical (sponge/floss) and biological (surface area for BB) on all my tanks almost exclusively. The only exception is Purigen or maybe some other product if I'm having a particular issue w something. But its very rare that I use any chemical filtration.
Looks like you have your bases covered with that filter. What else would you like to be in there (and why)? As far as efficiency, your filter looks good to go. I wouldn't add more to the inside. Adding a small prefilter sponge over the intake strainer would give more surface area for BB and prolong the life of the polyfill. That's the only real area of opportunity I see, but not absolutely necessary.
92% of all statistics are made up on the spot.