Review: The Heat Company Handwarmers
These are perfectly ordinary disposable handwarmers. Nothing wrong about them per se.
In and out of the packet (Own work. License: CC-BY-SA.)
Except with the marketing, of course. They claim that these last for 12 hours. Maybe with a precise thermometer you might detect some faint memory of heat radiating from these after 12h, but in practice these become useless at around 6 hours, that is the normal time for other brands as well.
So these warmers are no worse than others, but doubling the time claim is just cheating the customer. I recommend supporting a vendor with more realistic claims.