I own a G42 and have shot and handled a P238. In fact, I got some pics of the size difference between the G42 and P238. Some have an LCP thrown in because I was comparing it, too, so just disregard the LCP in those pics.
I absolutely LOVE my G42. Although it is a little larger than the LCP and P238, it shoots like a dream. Recoil with FMJ practice ammo is practically non-existent. It recoils about like my Ruger MKII .22 pistol. With good JHP ammo, recoils is just a touch more, but not much at all. When I first got it, I had my wife and daughters out at the range with me. I handed my 12 YOA daughter (who is very small for her size, about the size of an 8 or 9 year old) the G42 and she loved it, too. She was kinda mad that I wouldn't let her have it. Recoil for me was very similar to the P238 I shot.
I honestly couldn't believe how accurate the G42 is for how small it is. The real sights, compared to the pretty much useless nubs on the LCP it replaced, really help with accuracy. Again IIRC, I found the P238 a little more accurate than my G42, but not by much.
I am 6'2" and have pretty large hands (just shy of being able to palm a basketball) and the G42 fits me very well. Try handling one before you buy, but I don't think you will have trouble with it. As stated above, if Hickok45 can shoot it well, you should be able, too.
Although the G42 is a little bigger than the others, I am able to pocket carry it. I know you were looking for AIWB, but it should give you an idea of the size. The G42 is at the upper edge of being able to pocket carry, but it is doable if you want.
Now for some pics.
The G42 with the P238. I lined up the rear of the guns as well as I could. Don't mind the stupid "diamond plate" finish on the P238. Not my gun.
The front ends of the G42, P238 and LCP (I told you there were some with the LCP, just disregard it). The LCP is the shortest with the P238 just a touch longer, then the G42. The barrel and slide on the G42 are about 1/2" longer.
The LCP, P238 and G42 lined up with the tops of the slides on an ammo box and not resting on the sights. Myself, because of the absolutely tiny sights on the LCP, I think that sitting them on the sights doesn't present an accurate representation of the overall size. As you can see, the G42 is a little taller than the P238, about the width of the mag baseplate.
A shot from the rear with the guns resting on the tops of the slides.
As for weight, IIRC, the G42 is a little lighter than the P238. Not much, but a little.
Myself, I tried out a G43 when they first came out because I was thinking about going with it instead of the G42. Like I said, I pocket carry the G42. The G43 was just enough bigger than the G42 that I couldn't draw it well from the pocket. Also, although it is just the way the gun fit me, the G43 recoiled directly into the thumb knuckle in the web of my hand. It physically hurt for me to shoot it. If it had been small enough to pocket carry, I would have sucked it up and carried it anyway because 9mm trumps .380, but it didn't. If I have to belt carry, I already own a 9mm Shield that I love, so for me, the G43 was out. Moral is to always try (if you can) before you buy.
Hope that helps with your decision. Good luck.
Bub75