Throughout the set the design has a pre-worn leading edge for better turf interaction and a bottom heavy sole that sees the lower half of the head have a 'J' look to it from the toe side.
This is what gives the AP3 it's forgiveness and launch and the face construction gives it the speed. The lofts in the 3 to 9 iron are 1° weaker than AP1 so you will need care if blending the sets.
You can also blend the AP3 into AP2 sets, but again the AP3 are 2° stronger in 3-6 irons and 3° in 7 to PW so it is possible, but you may end up with two clubs of the same number from different sets that have different lofts.
In those short and mid irons the sound and feel is excellent and if you are used to the feel of the forged AP2 then I don't think you will notice much difference, apart from the fact that they are more forgiving.
It really is very easy to slip into the 718 AP3 if you have used AP2 or TM-B in the past, as it looks the same, but is bigger, without being oversized.