Fantastic little player. I'd never ever complain if we signed someone as brilliantly watchable and talented. But I don't think he's what we need. I don't think he's actually what a lot of people on here really want, either.
This is not a player who will give you more control in midfield. He's a battler. He gets half a foot on every ball, even when he has no right to. He manages to keep dribbling even when he's riding tackles and fouls and half-losing the ball. He stays in the fight for the loose ball and his quick feet and quick brain shine when it's a real melee in midfield.
But compare to Mainoo. Around Mainoo, there are no loose balls: either he makes it his, quickly and cleanly, or he correctly judges that the opponent has it, and he stays right side of them and defends. If the dribble is going to force him to ride tackles and fouls, he doesn't dribble: he passes or turns or shields instead. He doesn't win a melee in midfield, he prevents it from becoming a melee.
To be very reductive, Neves is a Klopp player, and Mainoo is a Guardiola player. Neves will thrive on transition, and create more, and probably do more individually. Mainoo will facilitate team dominance, crank up pressure, reduce risk. His 'every touch' videos will be better than his highlight reels.
You might say the two would complement each other, but I don't think so. I think they're stylistically at odds. Neves would destabilise Mainoo. Mainoo would dull Neves.
The player to complement Mainoo is a Rodri type. Positional discipline and nous to complement Main's ability to play equally confidently across the entire pitch. Grit and 'defence-first' mindset to complement Main's purity of style. Carefulness with possession to match Mainoo's.