It'd be more helpful if you could condense an 11 minute video into a couple paragraphs of text, but I digress.
Ness generally has several other options that are less risky and more rewarding than using Magnet's windbox. It sounds good on paper but for example, you could only feasibly get a Uair or Fair from Magnet, whereas several other safer options (dash back, SH/FH back) can net you those and much more (think PKF or your own grab).
If you had a hard read (and you'd probably need one to try the Magnet thing - it's rare for someone to just run up and grab in the neutral), you could even dash back and pivot tipper Fsmash them in the face. Windboxes are also invalidated by shields so if they approach with a running shield (not unheard of) you'll eat an aerial OoS during Magnet's lag. If they approach with an empty SH they might get pushed back slightly, but it's likely you'll still eat a spaced aerial, since they can react to Magnet.
Basically what I'm saying is that the risk - reward is not attractive compared to Ness' other established options, since it's not quite safe and the most you can get out of such a read is one or two aerials.
As for buffering a pivot (Dsmash out of Fair), that's not really a Ness specific tech and it's not really new either. It does have some use though.
