Been using the 6 Plus now for ~3 hours and man it is so nice, the big screen with the black phone and case really pops!
I can use it with one hand no problem, the top corner icon is a stretch but if I adjust my grip slightly it is fine.
What I have done is moved my apps about so the frequently used ones are easy to reach and I haven't even been using the double tap feature at all since doing that.
Two hand use is excellent, webpages on Safari look great and the iPad style Mail and Messages is a nice feature.
WhatsApp needs an update though as everything is massive!
Football tomorrow so good afternoon out with it, will see how it feels in my suit jacket pocket.
And the Apple leather case is brilliant, without it the phone is a slippery devil!