Values listed in brackets are for alternate (secondary) fire.
Dual MK23s provide a higher rate of fire and magazine size than their single equivalent, but at the cost of a lack of iron sights. With potentially lower accuracy but more damage output, their role is more suited to a backup weapon rather than a side arm, to be used in panic situations.
With the long reload time, it is best to keep your magazines full for when you need them.
While they can be effective over a long distance, the lack of iron sights may be a hindrance for some. If so, consider sticking with a single pistol or reserving the weapon for close combat.