Black holes naively look like a great way to get 100% mass-to-energy conversion, but when you really look into it, things aren't that great. To get more energy

Black holes naively look like a great way to get 100% mass-to-energy conversion, but when you really look into it, things aren't that great. To get more energy output, you want the black hole to be small (to have a high curvature in the event horizon); but, black holes that are small enough to give reasonable output are also too small (smaller than an atom) to reasonably feed new matter into. Meanwhile, black holes big enough to feed fuel into have an incredibly terrible power-to-weight ratio. And that's assuming that black holes even work the same way when they get that small. Quantum gravity could easily screw things up even more (or make them more convenient; who knows?)