Routt hasn't played up to his contract this season- as anyone who watched him get abused by Vincent Jackson and Mike Williams can attest. This does not mean to say that he is worse than all of the corners on the Buccaneer roster.
Eric Wright is now the best cornerback on the team with absolutely zero depth behind him. Leonard Johnson has been serviceable these past two games though his longevity, dependability, and improvement are uncertain. If Johnson goes down, Myron Lewis will be seeing a lot more playing time and nobody needs that.
Routt is built similarly to Talib at 6'1'' and hovering around 200 lbs. He is supremely fast and will certainly be an upgrade over Biggers and beyond. It would behoove Tampa at the very least to see if he's healthy, especially considering there isn't anyone else on the market with his kind of potential or experience. He'll also come cheap.
Bucs fans find themselves in uncharted territory with a undeniably dangerous offense and a terrible defense. It's pleasant that Tampa knows how to stop the run, but that is of no consequence when they are invisible against the pass. Adding even a borderline talent at the position of most critical need is a must in order to secure more victories.