Yeah and a slow peak discharge rate is not really a positive.
We have some LiFePo batteries at work and we simply don't attach the full load they could serve, so they last around 10 hours instead of only 4. Going slower is never an issue I'd say.
Probably the real strengths are in the cost per Joule stored, but they are failing to make their argument properly.
Since it's a fungus, I would expect there is no issue, just like eating any other mushroom. Plants are alive too; that's not the important category from a vegan perspective, I'd expect.