yeah the small battery on the S6 can be a issue, surprised that even with a samsung Enoxy processor it lagged! Hopefully S7 will a leap better than before. I have the Mate 7 it also a 6inch display, it is a big phone no mistake there and honestly I bought it purely because I wanted a phone with fingerprint scanner at a lower cost and it had the best fingerprint reader of any phone beating iPhone and Samsung compleatly out of the water, plus unlike the other two you can't lift finger prints off the phone, good for the self concious people
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personally I have grown very fond of Mate 7 and Mate 8 will be a improvement as well. I bought Mate 7 for less than £300 Brand New but it came from Hong Kong. All round it has yet to let me down.