I think he'd be a quality running fullback. The question is around his work rate, playmaking and general decision making.
Who are the best running fullbacks?
Teddy, Papenhauzen, Laurie, Walsh,Latrell,Turbo,Ponga I would say.
The thing is Teddy,Papp,Laurie and Walsh have exceptional acceleration. Latrell, turbo and Ponga have quite good passing games and awesome foot work.
Crighton is a powerfull runner. But is he explosive like Walsh or Teddy. NO. Unsure on his passing game and footwork.
I do recall when he played fullback for Penrith his defense was caught out. Of course he will learn. Also how good does he organise the defensive line?