... Volume sliders are a terrible idea and especially with anything that has high power output. Wish the E series hadn't been botched so much. So many problems.
I won't say slider by itself is a terrible idea, but the way it was designed (*slightly sticking out on the side) does make it more problematic. If it is recessed and not easy to push on, I'll think it is completely fine for my taste.
p/s: As I view through the Z Review's video, many issues / complaints seems to cause by the reviewer's lack of interest to read the user manual carefully (or even the box, when he is referring the lack of mentioning of mic though it is clearly printed on the box).
p/s 2: I don't think there is a 'hidden DSP' so to speak - but I do notice a volume lowering when enabling the audio enhancement option. My guess is Window is basically lowering the digital headroom as a safety precaution to avoid clipping.