After a day of use I can say that I am very happy with the 6+ and wouldn't want to go back to a smaller screen. Already the 6 feels too small and my 5s by comparison feels completely tiny (although having tried larger screens before it always has to me.)
I have been able to do a decent comparison between them, I got a 6+ and I bought a regular 6 for my missus.
I'm 6'3 and my other half is a good foot shorter than me so between us we cover both sides of the fence. She thinks the 6+ is just crazily big and struggles to hold it comfortably and steadily to use and thinks she would just constantly drop it and that's with two handed use.
I've got pretty big hands (my smallest finger is a good bit longer than her biggest finger
), I can easily wrap my hand right round the 6+ and in use I can reach from the bottom of the screen to the top with my thumb. In fact I can reach anywhere on the screen with only minimal grip adjustment and I think that once my case arrives and I'm not babying the 6+ so much, that'll become even easier.
I think there is naturally going to be varying opinion when there is such a difference in both screen size and the size of the device. And thats good, we wouldn't want to be all the same now would we?
I love the 6+ and would happily recommend it. But I would caution the petite amongst us, with dainty little hands and no experience of large screen devices, to either try the 6+ or another large screen device first. Because you may find that for you even using two hands becomes a little impractical when you take into consideration things like, walking down the street while texting.
So really and not at all surprisingly I think the real questions are, is the 6+ too big? No. Is the 6 too small? No.
It is simply a matter of preference and ones ability to comfortably use a device. For some the 6+ is definitely too much to handle (literally). While some, like me, will welcome the change and say that finally Apple have made a device which feels like the right size for my hands.
