I have, in great detail.
He takes a great set piece, there is a value to that.
However for every set piece he takes for us you have to realise that that takes a goal/assist away from Baines/Barkley/whoever.
So lets say under Sig we score an extra 4 goals from set pieces than we would have otherwise. That would be good, in the PL a goal is worth roughly a point on average. 4 extra points could be CL qualfication.
However we also have to consider open play. In those terms he doesn't produce as much as you would hope 4/5 goals and similar assists in a whole season playing in a front 3.
That is a big problem for me. In open play he is nothing special, even allowing for the team he plays in. When the likes of Wayne Routledge and Marrou Barrow are making twice as many chances over a season, in the same team, as a player we are going to splash £50m on then it is a worry.