The 32-year-old's move was finally completed on Thursday morning, signing a deal until the end of the season after impressing on a two-week trial in South Yorkshire.
Becchio's fitness has been a key issue for the Millers as the striker has not played a first-team game since September 2014 due to a heel injury he picked up when on loan at the New York Stadium.
While Redfearn admits that Becchio is looking sharp, he is not prepared to throw him into his starting line-up for Saturday's trip to Cardiff.
"He is a real quality striker. He is a proven goalscorer," Redfearn said. "He is a target perhaps we haven't had so he will allow us to play a little bit differently.
"We are going to secure the ball a lot better with him around.
"He is a bit off a start, but he is definitely off the bench.
"He had a game behind-closed-doors against Sheffield Wednesday on Tuesday, played 90 minutes, score so he is in a good place.
"He knows he is a little bit short of match fitness but he is getting there really quickly. He has worked hard in the last couple of weeks. He is not too far away at all."
