I've seen Darwin play quite a few times for Benfica, and from the very start I liked him but was a bit wary - his talent is very raw, you can see he has the physical ability and work rate to do wonders, but I thought in his first season that technical ability often let him down, and he just didn't score enough.
That changed this last season though - he scored about a goal per game in the Portuguese league and obviously also did well in the Champions League, scoring against not just us but other big clubs before. So he seems to have turned a corner, and become a lot more consistent. On paper, it makes a lot of sense. It will come down to what other players we could potentially get given the price.