"It's a fantastic opportunity for me here at Shrewsbury," the full-back told BBC Radio Shropshire.
"Since leaving Birmingham it's been a slow downward spiral since then at Watford. It's a chance to prove people wrong, which is what I'm here to do."
Sadler made his Birmingham debut aged 17 in a League Cup tie at Leyton Orient in October 2002.
An ankle injury limited him to 52 appearances for Blues before his move to Watford, where he played 35 games.
Sadler believes he will enjoy the experience of playing for Shrewsbury as they try to battle their way out of League Two.
"It's a fantastic club and they have a great stadium, there won't be much better for a player to enjoy his football and hopefully the fans will get behind us," he added.
Source: BBC Sport
Source: BBC Sport