*cracked record post* Bad neck, limited rotational range many many years of testing and using mirrors to find ones that allow me to keep cycling urban Manchester and fast rural pennine etc roads with confidence and in safety.
Zefal Dooback is the ultimate mirror for flat/cowhorn bars.
Sprintech Bar end mirror (page 1) is the best for drops.
Zefal's spy and spin are fantastic mirrors that you can fit to pretty much any bar type. NB the Spin is a bar end plug type, so butterflys are out, although it is effective on drops as a plan B after the Sprintech bespoke type.
The Spy is a fit anywhere, any bar mirror. I've even used it around the hoods of a roadie.
The minor (& it is minor) drawback of spin & spy for someone quite reliant on a mirror is their image size, you do need to give them a look rather than a glance. Dooback and Sprintech are big enough for a flick of the eye to give you all the distance and speed info you need.
All of them though will allow you to see that tell tale glimmer of movement behind purely in your peripheral vision, cueing you to take a look and be aware immediately that something is approaching into your zone
I would never advocate a mirror on an arm and have never found anything Blackburn make to be above gimmicky level, similarly the popular round cateye one, while it is a bar plug, it has a loose & weak ball joint and you can't get a proper vibration/air resistance free image out of it.
I recently had a bike-eye from a fellow forumite who found it useless & I totally agree, you can't use it with most rear luggage or a good size saddle bag nor without screwing your pedalling up by craning your leg out of the way, like a motorbike racer taking a sharp bend, every time you wish to use it. One to be avoided IMO.
& usual caveat, yes I do twist my head as far as I can before a manoeuvre as a visual cue to a following driver but by that time my ears and mirrors have told me what I need to know to be safe in my own actions & since my 1997 neck injury necessitated mirrors, I've never ridden into/near missed a following vehicle through my own lack of head mobility.
Edit: +1 to a good road position & anticipation too, never be in a position where you find yourself potentially stuck behind a parked car, obstacle etc or making a last minute dive out to avoid such.