I don't see how such a product would be useful for anyone. At least in USA, anywhere a 25A circuit is available, a 15A circuit is also available. The converse (using a 25A device on a 15A circuit) would be useful, but also wouldn't be dangerous in any way.
Looking at us (NEMA) plugs, there's plugs for 15A, 20A, 30A, and 50A. I'm going to assume everyone means 30A instead of 25A.
Generally, where there's a 30A circuit, a 15A circuit is also available, but there are exceptions. You may have wired a RV hookup with only a 30A receptacle, but you want to run some lights, or tools or ? with a 15A plug from that on a temporary basis. The circuit is (presumably) good for 30A, so adapting to a lower amp receptacle is reasonable --- it won't hurt anything to draw fewer amps through the circuit.
Adapting from a 15A socket to a 30A socket can be dangerous; the 15A or 20A[1] breaker or fuse on the circuit won't immediately open with a 30A draw, and the wiring will heat up during the time it takes for the circuit protection to open; possibly long enough to cause a fire. Of course, just because a load has a 30A plug doesn't mean it draws 30A all the time, there are conditions where using such an adapter is safe, but it requires knowledge of the load.
[1] US NEC code allows for a 20A breaker on circuits served by 15A receptacle, as long as there is more than one receptacle
