I have seen video clips of people making this work. Of course video is capable of showing all sorts of things that only partly match reality. The only reason I don’t question it much is that for the blow dryer/dry ice method, no one is selling anything. I have no reason to think that someone is doing the “Ding King” advertising tricks.
Anyway, I’ve not tried it either. The negative thing I’ve seen people say has to do with unknown effects of the dry ice on the paint.
If I were you I’d pick one of the dents in the least conspicuous area and give it a whirl - a tiny bit of time & money is pretty much all you have to lose. If it does anything really bad chances are you’ll be headed to a body shop anyway.