I've been using a Hafny bar-end mirror and a Varia radar unit for a number of years and have been extremely happy. Some may think a mirror and radar unit are overkill, but I have no issue going overboard with safety. The Hafny bar-end mirror is super easy to install and stays in place even after going on a rough road. The Varia radar unit is something that I will not ride without.
Hafny Bike End Bike Mirror, Adjustable Convex Rear View Mirror for Bicycle, Clear HD Glass Lens, 360° Rotatable, Fits MTB Road E-Bike Scooter, HF-M951-FR03 (1pc Silver Glass, 62mm Dia) https://a.co/d/0f3M9Mhh