It wasn't that bad for me and I have really small hands. I can use the 6 one-handed okay, but it is slightly too big for me to reach all the way across the screen with my thumb. I actually don't use reachability at all, the biggest issue for me is the width of the phone not the length as most of my one-handed use is web-browsing where all the controls are at the top of the page. I've noticed that I shift my grip instinctively when I'm moving my thumb across the screen, but it took a little while before it felt natural to do so. I do feel a slightly smaller phone would feel more natural, but I don't think I could go back to the screen size of the 5.