This mod tweaks Arc Furnaces and Ingot/Plate/Gear Foundries to be able to use non-Efficiency modules so they aren't strictly inferior to regular furnaces in the end game. Specifically:
Arc Furnaces and Foundries can use Speed Modules. Note that Foundries still don't have module slots so beacons are needed for them.
Arc Furnaces can use Productivity Modules when melting base metals (from ore, crushed ore, or pure ore, so no alloys). This is to match behavior of regular furnaces, which also only allow Productivity Modules on those recipes.