The main difference is that it would be moving from non-renewable sources to renewables. As well as that, the methane is already there being released, it’s just right now we don’t use it and instead a large portion of the world just dumps it into the ocean or rivers untreated. So it would be turning human waste pollution into fuel and fertilizer instead of contaminating water sources and releasing the methane.

In cold climates, heat pumps don’t work when it’s gets to -40c, so people who own them have gas furnaces as a backup. The same happens with electric vehicles; their range drops with the temperature, and some stopped working a few days last winter.

SO that’s why human waste is considered a “transition fuel.” It’s an option to supplement other energy sources until we have what we need to transition away for good.