Redknapp worked with the English striker at QPR and has backed him to succeed at Southampton.
The former West Ham United and Tottenham Hotspur manager has also claimed that he understands why Rangers had to sell the 26-year-old in the January transfer window.
“Charlie Austin will fit in well at Southampton, and Queens Park Rangers just have to accept they took a gamble which didn’t pay off,” Redknapp wrote in The London Evening Standard. “QPR supposedly turned down about £13million from Leicester for him last summer on the basis he could score the goals to get them straight back into the Premier League.
“He has scored 10 in 12 starts this season — which is a pretty good return — but they are 15th in the Championship and his contract is up at the end of the season.
"In that respect, £4m is not a bad deal from them but it’s a better one for Southampton. Their style of play will suit Charlie, they create a lot of chances and I can see him having a positive impact there.”
Austin has struggled with injuries this season, but he still scored 10 goals and created 17 chances in 16 Championship for QPR.
During the 2014-15 campaign when Rangers got relegated from the Premier League, the 26-year-old scored 18 goals and created 23 chances.
The former Burnley star showed last season that he can succeed in the Premier League, and Southampton fans should be optimistic.