I quite like Onana and think he'd be a good upgrade on De Gea. My first choice would probably be Diogo Costa but if Porto won't budge on price then I'd be happy for us to pursue Onana if he's gonna be significantly cheaper
I think each choice has to be even more budget friendly than previous years. The Gaffer will not have the room to blow the budget that he was able to push last year (that's what it felt like last summer).
Also, I do think that the 2 young midfielders is a good thing, at a bad time for it too leak. Good teams recruit for now, but also for the future. Example: we had nobody to replace Carrick, went for EOL (end of life) Matic, and ... void... There should have been recruitment for a young player 3-4 years before Carrick turned 30. Same with Matic...
So, it looks awful that we have "nothing" in the basket but some young pups, but we need balance.
I'd buy him in a heartbeat. Ten Hag knows him really well, he'd improve our buildup instantly and his shot stopping is equal to De Gea's. Not sure he's got the worldies in him like DDG but overall it's an upgrade.