Just about finished watching the Udinese/Atalanta game - Castagne is not a terrible footballer, seems to have a decent engine, gets up and down and does support attacks well, offers himself up, in the first half his recovery pace seemed pretty decent, a couple of times they were hit on the break and he sprinted back to get to the attacker. Second half that recovery pace seemed to get a little less. Clearly more comfortable on the right, on the odd times he did get into forward areas he doesn't seem like the sort to take someone on, I don't think he's got a change of gear like that, but he gets his head up and tries to choose an option or find a pass/cross rather than than an aimless head down cross to nowhere.
I saw someone describe him as a bit of Davies, I would say possibly a tad better, but I get the comparison on this look.