A good signing for me. Good player (just how good we will find out in the coming year or so), young and english. It's nice to see we're building for the future and taking the long view.
People saying we don't need to strengthen the backrow, what about when Fitz leaves? Plus we're short of props which suggest we'll have to move a SR up to prop which then leaves our SR light. Also if we'd waited until he was available on a free you can pretty much guarantee he'd have gone elsewhere.
Whether he is worth our rumoured fee, only time will tell. If he fails to live up to expectations then Cas will be laughing but if he fulfils his undoubted potential then it'll look like a bargain. Either way it's too early to pass judgement IMO.