Emiliano Martinez might be an option for Man United's problems, but it won't last long because Martinez is no longer young, and from a business perspective, it is also less promising because Martinez's price is still quite high, and it is clear that his transfer value will decrease every year after joining Man United. This may have been a tough decision for Amorim as he opted to go ahead with the speculation by signing Senne Lammens.
Senne Lammens is indeed young and much cheaper than Martinez, but he has no previous Premier League experience, and there's no guarantee he'll perform better than Onana or Bayindir.
Many people are actually been over shadowed with the penalty heroics of Martinez and have failed to look at him in the last two to three seasons because he has actually been a disaster, if you look at the stats he has actually had more errors leading to goals than Andre Onana which definitely looks like he is actually past it. Manchester United going for him will be like having three goalkeepers with same ability. Also the wages and the age of Martinez was definitely the most worrying factor in this transfer and I seriously support Manchester United in looking at other end.
Signing Lemmens was a huge risk but I would still take the risk over having Martinez in the squad or leaving only Onana and Bayindir, the arrival of a new goalkeeper will be actually a good one as it will create competition between them all