I bought an iPhone 6+, mainly because it's almost exactly the size that I've been wanting for an ebook reader for years.
I was nervous during the week between ordering it and its arrival; despite my attempts at making paper mockups, it seemed plausible that it might just be too big for me.
But when it arrived, it turned out to be a good size for me.
(Shortly after it arrived, I noticed that it was nearly the same size as another item, so I made a little movie about that. (30-sec video; you may have to turn up the volume to hear the sound.) That's on Facebook, but I think it's publicly viewable by everyone. If not, lemme know and I may upload it to YouTube or something.)
The 6+ is especially lovely for ebook reading. I compared iBooks on the 6+ to iBooks on the iPhone 5s and on the iPad mini; I found that (at a font size that's comfortable for me) the 5s shows about 120 words/page, the 6+ shows about 220 words/page, and the iPad mini shows about 350 words/page. Which means the iPad mini is very close to an average mass-market paperback in terms of words/page, but the device is wider and higher than a paperback, and it has much wider margins than a paperback (at least in iBooks). So the iPhone 6+ seems to me to be an excellent compromise for this purpose; about 2/3 as many words per page as a mass-market paperback, and fits easily in my pocket.
It's also lovely for showing Apple Maps or Google Maps on the car dashboard. For the past couple years, I've been using a ProClip modular dashboard mount; you buy a clip that's specialized for your car model and a mount that's specialized for your phone, and you attach them to each other. I like that well enough, but I just discovered the Kenu Airframe+, which is a one-piece and one-size-fits-all mount that attaches to most cars' vents and holds most phones, and can be carried around in your pocket. So that's my new favorite dashboard mount. And it shows the 6+ screen to excellent advantage. It gives me a small taste of what Tesla's giant dashboard displays are like.
I know that a lot of people have said the 6+ barely fits in their pockets, and a very very small number of people have reported the 6+ getting bent in their pockets. (Consumer Reports did some tests and, iIrc, found that the 6+ is less subject to bending than the 6 or the 5s.) For me, none of that's been an issue. It fits easily in my front pocket, and the way I walk and sit doesn't put any pressure on it that could bend it.
I've also seen several reviewers report that it's slippery and easy to drop. That hasn't been my experience at all. With both the 5 and the 5s, I dropped them for the first time within a week or so of buying them; with the 6+, I didn't even have any particularly close calls in the first two weeks. I've had several close calls since then, but I think have only dropped it once, out of my shirt pocket. (It does not fit comfortably in a shirt pocket, but I still sometimes carry it that way, around the house, for convenience.)
One reason that I may be having less trouble with it than some reviewers have had is that I don't normally try to do things like texting with one hand. A lot of iPhone operations are two-handed for me. I do sometimes hold it in one hand for ebook reading and probably some other tasks (I haven't kept close track), but when I do hold it in one hand, I don't normally wrap my fingers around it; the phone rests on top of four fingers, and I tap and swipe with my thumb. I think that was how I tended to use the 5s as well, but I'm not sure; it feels very natural and unconscious most of the time, so I'm not thinking about it a lot. That grip does mean it's hard to press the home button while holding it one-handed, though. It's also probably a less secure grip than wrapping fingers around it would be, but again, dropping it hasn't really been an issue.
Someone I showed it to suggested that it's almost more like a mini-mini iPad (an iPad micro?) than like an iPhone. I agree, and that's a lot of how I'm using it, to the point that I get a little unreasonably annoyed by the ways in which it doesn't behave like the iPad mini. For example, Google News in Safari displays the iPhone version (which I don't like) instead of the iPad version (which I do). So I'm still using my iPad mini for various things around the house; but I'm now even less likely to carry the mini outside the house than I used to be.
I had occasion to pick up my 5s again after a couple weeks of using the 6+, and was struck by how small it seems. So I guess I got pretty used to the 6+ pretty fast.
The one way in which the 6+ does still feel too big to me is when I hold it up to my ear to use it as a phone. That makes me very aware of its size, and a little self-conscious about it if I'm in public. But I'm getting used to that over time. And anyway, much of the time when I use it as a phone, I'm using it with earbuds or a headset, in which case holding it up to my face isn't an issue.
It's definitely not the right phone for everyone, and I'm still sad that Apple is now not serving the needs of people with smaller hands. But so far, it's a very good phone for me.
(Wrote most of this entry in early October, didn't get around to posting it 'til now.)