I'm still undecided if he'll be any better than Cahill (the stats according to CIES suggest not yet), but his ability to play across the back 3 and at full back means he's effectively a replacement for Ivanovic, Ake, potentially Zouma, and perhaps even Christensen if he doesn't make the grade next season.
http://www.football-observatory.com/-Ratings-eng-?code=65602
His 'rigour' and 'recovery' numbers are worryingly low for me, 60 + 38 v Cahill's 80 + 38. Hopefully we'll see an improvement next season.