There’s this almost common occurrence in Nigeria for car broken side mirrors to be replaced with plane mirrors. This is a potentially dangerous thing to do because plane mirrors which gives a standard reflection, does not allow a driver an areal view of the surroundings when on the road. The reason convex mirrors are desirable for side mirrors is it’s ability to reflect a reasonably wider rear-side view of the car, increasing visibility of vehicles approaching the car from the rear.
In a car checking blind spot can easily be done by looking over your shoulder, in a truck, bus, or van this is sometimes impossible. The bigger the vehicle, the bigger the blind spot, which is why most big vehicles are equipped with bigger and complex convex mirrors.
Convex mirrors enables a driver to also see parts of the car like the rear tyre which is good for knowing when a tyre is damaged and also for avoiding hopping curbs especially for driving beginners. So when next your are replacing a broken side mirror insist on a convex mirror.