Oh also just thought of another angle that could become problematic like CO2 generation over the centuries has resulted in global warming: if that device only produces hydrogen from the plastic and not 1 oxygen molecule for every 2 hydrogens, burning that hydrogen will use up oxygen and create more water.

Compared to hydrogen produced from electrolysis that also produces the balancing oxygen and uses up water such that the ratio of H and O as well as the total amount of water doesn't change over time.

At small scales, it doesn't really matter, but the same could be said for basically any pollution and well gestures around. It didn't start out like this for any of them.