Reference:
A.
https://www.academia.edu/36217967/Su..._Mahdist_Sudan
In this exceptional reference are details on Sufi use of weapons and traditions dating back centuries. In fact the Luttis; a sect of the Sufi, used these weapons in gang fighting to good effect and were feared amongst the population. The paper discusses the influence of these decorated arms on Sudanese weapons of the Mahdi.
I think what is interesting is that such arms were used across regions spanning the entire Muslim world and not confined to any one country. In other words they went where the Sufi sect went. The lethality of two headed axes arises here and it may be that such weapons were only used for shock effect per se since the idea may not have been to kill the opponent but to suppress as outlined above by Ariel perhaps with a "bonk on the head" rather than to remove it!
Deaths however, were not uncommon in these Sufi groups against their enemies. They used other weapons to boot including clubs.. In using two headed and single headed moon shaped axes I doubt that the idea was to massacre the opposition.. as also noted by Kubur. Ordinary Sufis carried the axe as outlined in Reference A as a tradition.
In the case of the project axe at #1 typically the haft is given the reptile skin treatment . In the battle concept talismanic infused, decorated calligraphy, on arms at the time of Omdurman (not the Mahdi but by his successor) these axe heads and alam acted like battle emblems or flags meant to inspire warriors in the attack...augmenting the profuse decorated flags shirts and other weaponry on the battlefield.