I don't know if it's been suggested already, but if you use an auto-spawner, lead the mobs to a 3x3 area with an activator with scythe, and in the center a sewer with a 1x1 radius upgrade to pick up the experience and a vacuum hopper to pick up the items, you can make a mob grinder that basically only needs a few buckets of mob essence with looting. if you'd use the grinder from MFR, it'd only produce a bit of the mob essence that was used to spawn that mob, but if you kill them otherwise, for example with an activator with a scythe to get a 3x3 radius, they'll drop their full experience, and since a sewer can pick up experience, you can loop it back to the spawner and spawn more mobs. ofcourse this won't work if you spawn mobs with the exact mode on. another note, if you use this to spawn endermen, you can use their balls in an ender generator to produce RF, so you can power the spawner with that power, and the excess for whatever you need