Hey Andrew, think height of the child and size of bike/adult rider. My little one is 3.5ys, but is 105cm tall - so very quite tall for her age (she as the same height as an average 4.5year old). Mac-Ride say ideal for 2-3year old, but works for 4-5years. Think the increasing frame reach is helping as you can get them further forward.
You should def give one a go to compare to the Shotgun (also Shotgun do some nice mini handle bars to attached if you don't want to put little grips or bar tape)
Checked with SQLab as am looking the 12degs 3ox and they stated that to preserve existing position you should use a slightly longer stem as the 30x do not sweep forward first before the rearward sweep. Their 311 bars do have a sweep forward first to negate the need to fit a longer stem.