According to Wikipedia existing electrolysis systems are between 70-100% efficient. It's not fundamentally difficult to do (when I was a kid I made a "rechargable bomb" that would fill a balloon with hydrogen+oxygen and blow it up) but if you are doing it at scale you are going to be very concerned about capital cost and energy efficiency so there is room for improvement.
The important number when using hydrogen to carry energy is the round-trip efficiency. It has been hard to improve the efficiency of the energy-releasing side. We are fortunate that the number's importance is declining.
I don’t think the main interest is energy storage today, I think it is to replace other sources of hydrogen in industrial processes. Hydrogen as a fuel to say cook food or run a power producing turbine competes with many other energy sources and carriers but for industrial purposes there is often no alternative or the alternative is carbon heavy. (E.g. carbon monoxide is used to reduce iron in a blast furnace, hydrogen is substitutable for CO for many metallurgical functions.)
As cost to produce falls, it will be used in more places. Ways to store and transport energy will be among those.
LH2 is very attractive as aircraft fuel.
But I take your point: for other uses, the production efficiency counts more. Conversion to raw heat is pretty good, losing only what it takes to split the H2 and the O2, and then whatever of that heat you fail to direct to the end use, e.g. the steam that rises past the sides of your saucepan.
It competes with heat pumps for space heat, particularly given that air source heat pumps have gotten a lot better in 20 years. 20 years ago the word was that you needed a ground source heat pump in upstate NY but today air source heat pumps are completely practical.
Mine works down to a remarkably low temperature, but at that temperature is able to extract much less heat than the house needs to stay warm at that outside temperature. So I still burn a noticeable amount of propane, in bursts.
A fuel cell driving a heat pump is an interesting notion. The "waste heat" from the fuel cell is not wasted, here. If half the contained energy drives the heat pump at, say, 3x, you get 1.5x vs just burning it.
The extra expense of the fuel cell and heat pump seem hard to justify unless you have other uses for them. This is to say that hydrogen for home heating is unlikely to be important.
