As someone with an iphone that has 3d touch: it doesn't even remotely feel like the screen is going to break, or your fingers are going to hurt. You can also adjust the sensitivity on it. Pressing normally for a little bit longer time does something different (generally will bring up a menu while 3d touch will open up a preview window), and it takes just long enough to do that that it's uncomfortable. IMO it's not a necessary feature, it doesn't enable fundamentally new interactions, but it's really nice to have.

Ok, thanks for these precisions.