I fall into the later camp, my SE has been horrible since updating to iOS 11, Apple even replaced it under warranty and still its crap even after setting up as a new phone. Then you have others who come along "Oh my phones great, runs even better than 10.3" I can't understand it. It's not my phone as that's been replaced, it's not my apps as I only have 6 non Apple apps installed at this stage the only thing it can be is iOS. My phone runs fine its battery life that's taken a major hit, I used to get a full day and until about 6pm the following day with my usage on 10.3.3, On all versions of iOS 11 I will not make it past 9pm. Not even a full days usage.