Would this be our first loan with a right to buy ever as I can’t recall any? Cue about 20 examples being thrown at me..
Its probably the case, however its very much utilized everywhere in the world especially in Italy. Some big clubs got involved in it as well. Coman and Coutinho (Bayern), Pellegri, Saelemaekers and Diaz (Milan) and Morata and Milik (Juventus) are prime examples of it.
Its a win win situation for everyone really. The seller club are able to get rid of a player that no one really wants usually for a loan fee and with the prospective buyer's covering the salary. The buyout clause is usually kept low so the buyer would have ample incentive to give the player a fair crack of the whip as he might end up making a bargain out of it. That means that even if the player fails to make an immediate impact or the buyer is unable to buy him out, the loanee would get enough game time to maybe attract another club or have his loan extended.
In my opinion Dest's signing would be suited for such a deal. Barcelona aren't playing him so his price will go down, no one really wants to buy him and they need to offload unwanted players off their payroll. On United terms we would end up with a RB cover which would then allow us to sell AWB (whose price is going down as well). If Dest does well then the RB slot is sorted. If not then we send him back. Up until that time our negotiation team would have time to assess the situation and come to a conclusion (activate the clause or sign a new player)