depends on the situation, I keep a full one in gun, and a full one in holster's mag holder. Will it be enough?, probably if confronted with up to 2-3 attackers (many possible details aside i.e. distance, movement etc.), will it be enough to defeat a well armed mob in 2-3 vehicles? Probly not
. but its what I carry (better than nothing). So I say carry as much as you want, and are able to as you wish. (thumbs up)
BTW I speak of a Glock 26 with pearce grip/capacity extentions on each mag.
Oh, and that makes round count 26+1 tho' I have managed to push an extra round down into one of the mags.