Ighalo had a successful start to his loan spell at United after arriving from Shanghai Shenhua in January. The experienced Nigeria striker scored four goals in his first eight appearances in all competitions.
"He's a big United fan isn't he and he's done great, he's done really good, better probably than he could have hoped and Man United could have hoped and he's been a good addition to the team," Hargreaves told talkSPORT.
"I think all the boys are really good athletes and quick and want to run in behind and get the ball into feet but he looks comfortable with his back to the goal.
"I love Marcus and Martial, love their game, but they're quite different in the sense that they want the ball into feet and they want to run in behind, whereas he's comfortable being a target man with people behind him and then getting the ball and people can run off him.
"It's not always about getting the best name, it's about getting the guy that you don't have that you need.
"He was somebody that whoever signed him hats off to you, because he's given them something different."