around rank 36 you could duo almost all them if you have a gla or pug to tank the mob who is the same level. I personally didn't touch the nms until i was 40 and had a gla, we duo'd most them. The drop rate sucks on a lot of pieces, so you would want to zerg them and maybe try incapacitating them, (which people don't believe helps but w/e it's supposed to "increase likelihood of drops, and you can inflict this status all new nms)