I have Gen 3 26's, and all Ive put on them have been three dot night sights, which I add to anything that will take them anyway. Other than that, I would leave the gun alone.
I tried the Pierce extensions early on, and found they pinched my hands while shooting, and REALLY pinched my hand while reloading. More of a distraction than a help. Once you get used to your pinkie being wrapped under the mag, and using your middle and ring finger for the grip, I think youre going to find its very comfortable and the gun is very shootable.
The other problem with the extensions is, they make the gun bigger, which sort of defeats the purpose of the "smaller" gun in the first place.
While they are a little chunky, they are definitely smaller than the 19. I usually carry mine in an ankle holster, something I cant do with my 19's. I also have a Galco Executive shoulder holster for the 26 that works very well. I dont carry pocket gun in my pockets, so the 26 isnt going there either.
If you arent sure, Id recommend you try all three sizes and see what feels best and will work best for you. I have 17's, 19's, and 26's, and personally, I dont get the purpose of the 19's. Hey, its all a matter of personal opinion, and the only way to know, is to find someplace that has all three models on hand, and get them in your hands, especially side by side, and see what you think. If you can shoot them, even better.