Yeah fair.Not really.
The clause all clubs want is an option to buy at an agreed price.
If Ansu Fati has a great season and we have no agreed purchase price, then Barca reap the benefits when he returns to them.
If he has a rubbish season, then we simply don't exercise the option to buy.
Obligations to buy are different. They're just a ruse to delay paying the permanent transfer fee.
Loan with option the absolute best case.