The term "Active braking" specifies the braking for rotation of motor, I confirmed:
http://www.dji.com/product/e310 , sorry (but why DJI erases the description of active braking from this page!?). However, later lots of P2 had active braking, with E310 ESC/motors, 9450 props. My P2 is that version, and no problem to use both plastic/carbon fin, plastic/metal screw, DJI stock/third party.
But our local RC shop don't suggest use 9450L for P2 (E310) props for P3, because strength of the plastic differs (???). To summarize their words, there are 3 versions of stock 9450 props - "9450" metal screw for P2 (E310), "9450L" plastic screw for P2 (E310), "9450 for P3" with plastic screw. The third one is only suggested for P3, but that's not because of active braking (plastic screw).
If one would like to use carbon third party props, the metal screw is not problem, I think - but as others say, balance, vibration and quickness of operations maybe.