Benji isn't what he used to be but I reckon you can still get value for money from him. At the Dragons he had to be the man because their attack is so shit, but he could certainly be a good support player with Hunt, Milf and Boyd being primarily responsible for scoring the points.
I can only really think of him being a depth signing. Surely he's not ahead of Milf and Hunt. Having said that, we've had an extremely good run with injury with those two in the last 2 seasons. If one of them went down with a long term injury there doesn't really seem to be any ready made replacement coming through. You could play Nikorima, Kahu or Boyd in the halfs if you need to, but that would be weakening one position to strengthen another.
I did hear reports on the radio that if he is signed Hunt would go. Surely you'd keep Hunt unless there is more to it than that, such as a disciplinary thing or salary cap issue. Hunt would get twice as much as Marshall on the open market. Probably more.