Most would agree that front mud flaps are needed on the Model Y. Rear mud flaps on the Model Y may provide some additional protection. My observation is that the rear of my Model Y gets dirty from air and water flowing over the vehicle, not specifically from water and debris coming from the rear wheels. I.e. the benefit of having rear mud flaps on the Model Y is mostly for appearance. Some Model Y owners prefer the look of having front and rear mud flaps. Also, consider the Tesla PPF kit for the rear doors of the Model Y. There is considerable debris that can impact the rear doors of the Model Y even after installing the Tesla mud flaps on the front wheel wells. Finally, mud flaps on the Tesla Model Y do nothing to prevent your vehicle from being sprayed with water, salt, sand, dirt etc. from passing vehicles (especially from vehicles without mud flaps.)
To provide improved function the Tesla front mud flaps would have to be wider, i.e. extend outside the front wheel wells as with the Rally Armor mud flaps. You may not like the look but a wider mud flap would perform better.
