Fernandes and Lo Celso are almost identical, as far as playing styles go.
Put them anywhere in midfield, and they'll do a good job - they excel in almost every role. They're not pacy, but they make up for it by having immense amounts of stamina and good technical abilities to escape the press. They're creative midfielders, and they like to dictate play.
If there's a difference, it's in their histories and the intangible things. Lo Celso was a surprising success in Ligue 1 in a defensive midfield position, and then also succeeded at Betis playing all across attacking midfield (and at No.9).
Fernandes struggled in Italy in his early years, and only really exploded once he returned to Sporting Lisbon. But when I say exploded, I mean exploded - Sporting fans I know are *adamant* that he was literally the only reason they finished as high as they did, and his massive goals + assists figures bear that out.
Lo Celso is worryingly one-footed, and Fernandes is two-footed. And Lo Celso isn't really a set-pieces sort of guy, while Fernandes definitely is.
Either would fill an Eriksen-shaped hole. Both would give us a very strong midfield, even if Eriksen left.
We'll see how it goes, and if Levy manages to stop being a cheapskate for long enough to get at least one of them over the f*cking line.