The 35-year-old signed a one-year deal at Loftus Road on Thursday and trained with his new team-mates for the first time on Friday morning.
"I think he is going to be a fantastic player for the club." Redknapp said.
"He is a top-class guy. A great role model I think, I signed him as a 14-year-old so I know him better than anybody.
"He didn't need convincing (to join) - he wanted to come to QPR. He spoke to two top London clubs, but he wanted to come here and to play. He could have went elsewhere and maybe not played at times.
"I don't care what age they are - it's about staying in the Premier League. I took Rio - I'm not saying I'm going to sign all older players, but if they are good enough and can do the job.
"We are not going to spend fortunes. We will spend money on one or two players and pick up others on free transfers.
"We are not looking to splash loads of cash because we haven't got it. We want to make sure the people we bring in want to play for Queens Park Rangers, which Rio did. That was the key for me.
"He could have gone to Dubai or Qatar and earned a fortune. His wage demands were so incredibly low in my impression. It was an easy deal to do."
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