https://www.amazon.com/CIPA-11125-Hand-Mirror/dp/B000TCGD96

This is the mirror I’ve been using on my wrist. Works well for me so far.

However, there was a time when I was trying to raise my left wrist to check the mirror, there was bicyclist trying to quickly pass me on my left side and I almost back fisted him in the face.

I use a wrist mirror, won't give 24/7 peripheral view of your behind but it lets me see behind me when I need to without taking my eyes off of what's in front of me. https://www.amazon.com/gp/aw/d/B000TCGD96?psc=1&ref=ppx_pop_mob_b_asin_title

As for helmet mirrors I haven't used any and all the local riders near me use none or wrist ones, sorry