Make that double
But still have hopes he either returns to a Simeone-less Atleti or moves to United. He could definitely work in a Martial role, but it would help to have a more striker-y striker as backup. With players like Rashford, Bruno and Antony (or at least two of them), Felix up front could definitely work, but to be able to balance it out with the occasional second striker role would do wonders for him and the team. On the other hand, at times that could be Rashford, or they could switch positions during the game. I want to say Martial could be that guy, but even cloud-headed dreamy little me has to acknowledge that it becomes harder and harder to rely on his injury track record... Still an Martial FC member, but it's hard to see them play when most games are cancelled.
If United will be rich rich, getting both Felix and Osimhen (and Frenkie in midfield) would make them a title contendor, and possibly even a favorite, in a single summer. Other buys would be for solid backup, in my opinion, though having someone like Frenkie (or similar profile) would already be much better coverage for another Casemiro ban than McFredzersen are, and Dalot and AWB cover the right pretty well, with Malacia and Shaw on the other wing doing similarly. Perhaps a better Williams type for both sides would be helpful, but as a 3rd option on either side, that might as well be a youth prospect - if available - or Telles if he wants to stay around. And if you get Frenkie, you'll have more options to play with Eriksen at 10 (and Sancho - and Felix) in case Bruno can't. Rashford, Sancho, Antony, Garnacho, Bruno, Felix is plenty for the wings, and then Osimhen, Felix, Martial, Rashford up front and ETH will have plenty decision headaches ahead of him, and would have to try his best to make it suck. I can only imagine this happening, but it would be glorious.
TLDR: Felix is a good player.