Legality of a 25Hz camera depends on where you are. In most parts of Western Europe, for example, having a 25Hz or faster camera is OK. The question of whether it's OK to have an upgraded camera is the tricky one: even if the 'same' model is available in both low and high frame rates.
As far as I know you can (for example) export a <9Hz camera 320x240 from the USA to, say, England, with little-to-no paperwork. But the same camera hardware, loaded with 25/30Hz firmware, cannot be exported so freely and, at best, requires export paperwork and probably a certification by the end-user that they won't sell it to anyone Uncle Sam disapproves of. And if you buy the 9Hz camera, export it from the USA and then install 25/30Hz firmware, Uncle Sam is unlikely to be pleased.
(Similar limitations are in place with other countries; I merely use USA / England / Uncle Sam as convenient references).
For a ThermApp camera it's probably the government of Israel who might get upset, as Opgal is based in that country. That said, the sensor is made in France and its manufacturer (Ulis) may have contractual arrangements or legal obligations in place that means the French government would take an interest. It all has the potential to become quite complicated quite quickly.
As far as I can see the safest thing to do is to buy only a camera that's intended for use in your country - and, particularly if it's a fast frame rate device - don't try taking it on your vacation to
DPRK.