Well, could you check my math, then? (it's 3:43 AM here^^)
Because if it is right, one tank can store more than 3 redstone energy cells, not quite what I would call abysmal.
Sure, it might be worse than other systems, but it has the benefit not to have any additional cost to store the "energy", where the lava route needs nether rack to be efficient, so you need to spend some form of energy to mine it in the nether.
But as I have a big lack of sleep these days, I might be completely wrong with my numbers, and make quite big errors on calculations.