Might a fairer comparison of different synthetic-resin adhesives and fillers be simply by the applications advice given in their "operating instructions"? The manufacturers can't be expected to reveal too much but the Safety Data Sheets may be a guide to further comparing chemical and temperature resistance.
If anything I would suggest poor results with a product from a reputable manufacturer, more often than not are from poor use by the buyer. Manufacturers often say so, though a bit more diplomatically, in their small print!
It is vital we consider what we are using the adhesive for. It would be very unfair to blame it for failing if we subjected it to conditions outside of its advertised range, even if the manufacturer has allowed an unstated safety factor. Anyway as we all know, a safety factor is not an invitation to exceed the specified working maximum.
If the application approaches the adhesive's temperature limit we may need consider its ability to cope with the expansion and contraction of the surrounding metal; and this is deeply specific to the project's design.
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The filler types, like JB Weld, are synthetic resin adhesives mixed with granular or powdered binding agents, typically a metal or soft stone. These would affect the mechanical behaviour but might not affect the safe temperature range and chemical resistance, for example; although once cured from a correct mix these materials are remarkably inert within their safe temperature ranges. (Acetone will dissolve uncured resin, but dissolving the cured resins needs some pretty nasty compounds B&Q might not stock!)
At my work we used our own version for certain purposes, that blended slate powder of flour texture, with a low-viscosity 'Araldite' mix; in a recipe that had been tested properly for the right characteristics for the specific use. (I wonder if plain talcum-powder might work for a "home-developed" filler for some uses. Talc is a complex magnesium silicate, a mineral possibly among those typically mixed up naturally in slate.)
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I have not seen the video cited so can't comment on it, but as a general rule I would want to know if its creator is using the product as its own makers intend, in an application appropriate to it; and his working methods look convincing. Or of course, if the video is not simply a thinly-disguised advertisement!