Whether correctly I understand, that for switching on of this improving (cleaner shadows, smoother highlight rolloff, and cleaner ISOs) it is enough to only install Magic Lantern? Or need to include something "special" in the settings?
You need to set "ML digital ISO" to a negative value. This way you will see that in the live view the ISO value will turn green with a little "eq" next to it. But be aware that on very low ISOs the highlights get a little bit pink. You can color correct them or just don't use ISO 25 if you don't know how to remove the pink and you don't like how it's looking.
But it's a very nice feature to go that low in video mode
Thanks! Does on the improved features "cleaner shadows, smoother highlight rolloff, and cleaner ISOs" value of ML digital ISO? For example, the value of -0.2 is better than -0.1? Or simply put a negative value to -0.1, and value less than it simply changes the exposure (making the image darker)?
The exact behavior depends on many factors (picture style, contrast, HTP - as far as I know) so you need to see what works best for you.
My advice is to check the highlights with the RGB spotmeter - when they start turning pink, stop applying negative gain.