Some players dominate at a lower level, but struggle at the top, and some players go unnoticed at a lower level, but shine when they play with better players. I believe this is why clubs spend big amounts on scouts, analysts etc.
If United think Haaland can replicate his scoring form in the PL, we should try to get him in. If other top clubs also believe this, then his price will be very high. Think it's pointless to discuss what he's worth, as that will be decided after he has played for his new club for a while.
If we buy him, and he ends up scoring 300 goals for us, then £150 million would be good value. If we buy him for £20 million, and he scores 3 goals over two seasons and gets sold to Turkey, it's not good value.