The deal has raised eyebrows in some quarters as the player is not a household name in England.
Despite not being a recognised name, Niasse's form had made him one of the most sought after players in Europe 15 goals and seven seven assists in 40 appearances at Turkish side Akhisar Belediyespor.
He then followed that up with 13 goals in 23 games for Russian side Lokomotiv Moscow after a £4 million move.
Those statistics persuaded Martinez that Niasse was worth a gamble.
'Why the surprise?'
And the player's former manager at Akhisar, Hamza Hamzaoglu, has backed the signing in an interview with Turkish football website Fanatik.
“Everybody seems surprised but I am not at all,” Hamzaoglu told Fanatik.
"I guess those who actually understand from football agree that he is a very good player.
"We wanted him (at Hamzaoglu's former club Galatasaray) but it did not work out,” he added.
Goal stats speak volumes
Niasse's figures speak for themselves.
The striker has scored an impressive 132 goals in 235 games so far in his career at a rate of more than a goal every other game.
Whether he can replicate that in the English top flight remains to be seen.
But if he can hit the ground running then it could be just the injection Everton need to get their stuttering season firmly on track and perhaps launch a late assault on the European places.