The drop rate for the coloured beads of the Imps seems incredibly low. I had to spend over 8 hours killing Imps in order to get all 4 colours. This is far too long to make the quest enjoyable and just turns into a tedious grind.
If i remember i think it took me less than an hour to get all 4. It's RNG at the end of the day. Can always buy them off the G.E if people are selling.