All good points.
I would only point out the distinction between a deliberate shot when you want to fire the left barrel, such as to take advantage of a tighter choke or deliberate single shots with a DR where you want to avoid wearing out the right barrel and a rapid, instinctive 1-2 at a charging ele

I'll bet that regardless of how much you practice, the chap firing front/rear will be faster than the one firing rear/front.
You can't beat evolution - your finger moves faster pulled towards you than pushed away.
At the end of the day, to each his own though - better two triggers than one!!

just kidding