The reason for adding more blades is a matter disc diameter requirements for a given application.
Such as ground, fuselage or multi-engine clearance or to be able to deliver the power an engine/motor can produce given the aforementioned design constraints.
As far as your drone there is no need for them other than what some feel is a cool look which is only noticeable when static.
DJI has tuned the propulsion system (props, motors, ESC, firmware) for optimum performance.
Our Multi-Rotor machines work by balancing thrust against weight. Once that's achieved - then the forward / backward etc.. flight is achieved by varying one or more motors thrust.
This is unlike a conventional flying aeroplane that uses forward motion and its wing to lift ... the forward motion is either by gravity (Glider) or by motor / prop combo. Using different props can increase or decrease flight time by that change in thrust vs drag.
But our machines in balancing thrust / weight will adjust the motors rpm to achieve same thrust when you change prop design. But it is still same overall power demand - so no benefit at all. In fact you could result in reduced results.
Do not use aftermarket props no matter how much you'll save in doing so as you will have flight problems. DJI OEM props are 9443 0r 9450 and you cannot mix them. B&H still carries the 9450 props for $9.52 per set of 4.