They are very comfortable to use, but they cost double the energy. If you're still on coal power, you'll use twice the amount. If you pay more e.g. eff modules, or have the power to spare, yea they are great.
Once I had about 1k solar panels and three nuclear reactors with self-perpetuating enrichment, I shut down all the efficiency module production, ratcheted up speed modules and beacons, and went to town.
Even if still on coal power, I think the tradeoff of not needing to run coal belts everywhere makes them worth it
Yes, but you can finally stop using coal in smelters so more is available for power generation.