dot points since its easier and i don't leave a wall of text wihout spacings.
1) i like the iPhone XS Max, screen has better colors than my iPhone 8 Plus [which I handed to my mom, she likes it]. OLED is noticably better than iPhone X from memory, since apple doesn't overdo the vibrance/saturation on their oled displays to match the LCD displays [in terms of accuracy], but I noticed the new XS Max Displays are that much more vibrant without going overboard which is nice.
2) The camera is notably superior over 8 Plus, I can notice it immediately and I'm a dedicated photographer who uses a dedicated camera [i use a full frame DSLR + 85 f1.4 lens for portraiture since thats what I love photographing]
3) in regards to point (2), this phone will be good for many people [95%] at least who buy it that doesn't want to invest 4000aud++ on a proper dedicated camera but will want one that does the jack of all trades. Whilst I like the natural bokeh created by my DSLR, the iPhone XS Max comes quite close... altho the bokeh isn't as creamy smooth since it's AI/Machine Learning/Software bound but for a phone this is pretty damn good.
4) Adjusting from 8 Plus to Max is very simple. Don't overthink this part. It's just an 8 Plus with a little bit more real estate but with FaceID and better cameras and better OLED display. So if you like your plus phones, by no means go with the Max models. I myself did not notice much difference it felt like any other iPhone, since the form factor was equally close in terms of size jumping from 8 Plus, to MAX for a day, and back to the 8 Plus was easy for me if I had to go through a dilemma of pickin the two.
Likewise, if you are a camera junkie you'll love iPhone XS/XS Max. It's miles better than iPhone X even in terms of photo quality (I've tested iPhone 8 Plus and X but settled with the 8 Plus before because I felt both camera produced the same image without much notable difference that didn't warrant the X's purchase, but I can say the XS [and maybe the XR will have the same league too for a "budget iPhone"] are notable upgrades in the camera department.
As for one handed use. FORGET IT, anyone who talks about 1 handed use disregard their opinions. This is by means a 2 handed device [duh given the size] since reaching the top right will need you to shift your hand a little bit [but it isn't so bad as what most people say, you get used to it quickly]