Yoyo is more of a consistency issue imo. Calories in calories out is all of it. If you are yo yoing weight you are changing something at each end. I have always had that issue on diets until IF because life happens and you lose routine. With if I just dont eat unless I know its time, and my stomach is small so I fill up quicker. I bounced 230-270 for a decade. Now maintaining 190-200 and thats mostly water weight bouncing.
The way I see it, it's a good path to being able to move with less consequences to your joints. A bit like sugar free fizzy drinks? Are they good for you? No but if you can get to a healthier weight and then work from there they are a means to an end.
I think they're saying they're on a pendulum swinging between comfort/ discomfort. Low blood sugar sucks man. I don't know how they do it. I have a fast metabolism, and hypoglycemic. I'm a little jealous these guys can even DO this.