I'd be curious to know from people who are fans of the SE (like me) how they rank the following advantages it has in terms of how important each are for them:
1) One-handed usability
2) Pocketable size
3) Price
For me, that's how I'd rank those three. Price is a non-factor, and I'd happily pay a premium for a "Pro" level smaller phone.
I could go back to the 6/7/8 size, but it would still be a step down in terms of one-handed usability, which leads to a separate discussion which I've brought up a couple of times in the past:
They could do a better job of improving one-handed usability on even the larger phones. When they first increased the size of the phones, they introduced reachability, which was/is pretty awful. What they really need to do is rethink the UI altogether. A simple tweak would be to introduce UI guidelines (which they'd follow with the all of the built-in apps) which could discourage placing tappable UI elements towards the top of the screen. A better approach would be a completely rethought-out UI experience which made everything easy to do without needing to stretch your thumb to the limits.
I've heard a lot of people claim that they can use the larger phones "just fine" with one hand, but I call BS on that. I'm 6'2" and consider my fingers to be in proportion to my body size, so I'd imagine that my fingers (and thumb) are probably longer than most people's. Yet, attempting to hold the phone in one hand and swipe or tap on elements in all corners of the screen results in the phone often teetering and being close to getting dropped. The only way you can really do it is by holding the phone so that the screen is pointing almost directly up at the ceiling/sky, which isn't a realistic way to hold/use the phone much of the time. On that note, another approach to improving (but not solving) the issue would be to focus more of the weight of the phone on the lower half of the phone, which might reduce some of that "teetering" when trying to use it one-handed.