6 years contract? Hmm, seems like this player is ready to walk with Liverpool for every part of his career. I don't know but some of these long term contract has a way of back firing but I hope not with this player. With the amount they bought him I believe that alone comes with so much expectations with the fans waiting to see him do what he did in the Bundesliga, and if he doesn't deliver it becomes a problem but my worry is that he shouldn't be a one season wonder kind of striker and with less goals...well, Slot knows what he is doing for going hard on getting this player.
You see one of the reason why clubs go long term on transfer contract is because of the FFP rules, with the amount Liverpool has spent and with the wage load they have on their books after giving huge contracts to players like Salah and Van Dijke, they need to offer long contract to players so that they don’t break rules, it is not only Liverpool but Chelsea also give this kind of long term contracts to their players due to the money they have also spent on the player.
Also long term contracts are for players with huge potential so that when they hit their peak the player won’t be scouted by other clubs or leave early due to small time remaining in the contracts
For a player of Nicolas Jackson's caliber, Chelsea's asking price is clearly very high, even though they have benefited from the Club World Cup. Manchester United has set a modest budget in the current transfer window, having spent heavily on players last season, but the results were disastrous. This is evident in Manchester United's current transfer process, which demonstrates their careful negotiation, as evidenced by the two players they secured.
Chelsea are just trying to see maybe they can tempt any of the clubs to pay close to this price, Jackson is not worth this price and moreover Manchester United wouldn’t even spent such amount on a striker now and not to talk of signing Jackson with that amount.