It's all down to the prep at the end of the day.
I didn't use the gel (you gotta leave it on for a while whilst it works) But I Was impressed with the hydrate 80. I got a wire brush on the grinder for the backs of the outer cills, degreased tehm, dried them with airgun immediately and then painted that Hydrate 80 on. Been ina damp garage for 1 year with just that on. STill not re rusted whatsoever. Seems to neutralise any left and seal it off. Same with the front, rear wings on the bases, only hydrate 80 on them, not re-rusted at all. A £15 1ltr bottle will do a whole car too. The mastic paints are a rock hard paint so good against stone chips.
I went through same with looking at different things and you get put off by people not liking it. I imagine they are all good if the prep is followed and thorough.
If you just use normal primer it'll be rusty again in a year. Even Epoxy mastic paint on small items brackets I didn't use hydrate 80 on, have rust coming through again. Hence the reason why some people dont like some of the products - they probably didn't prep it well enough then blame the product for not working, so they don't like it or give a negative rating.