When I got back into riding earlier this year (sold our 10 year old Pedegos and bought some newer e-bikes), I went down on my first hard ride during a 'momentary lapse of concentration' while looking over my shoulder before making a left turn. Things happen fast at 20+mph! Right then, in a fair amount of pain, I determined that I was going to start using rear view mirrors!
I tested the Takealook brand mirror, both in the standard and smaller sizes. Would have been the least expensive solution since we have multiple bikes and would otherwise have to buy a bunch of bar-end mirrors.
In the end neither I nor my wife could get the good rear view desired with the eyeglass mounted Takealook mirrors. We ultimately 'standardized' on the Hafny HF-MR083 for our little fleet of e-bikes and now feel 'naked' and uncomfortable if we don't have one on the bike we are riding. More expensive option than the eyeglass or helmet mounted mirror, but gives us the information we need to safely be out on the road.
I've never tried a helmet mounted mirror, so can't comment on their effectiveness. But the bar end mirrors work, and work very well.