http://news.soxprospects.com/2017/04/scouting-scratch-rafael-devers.html
TLDR:
For his age, Devers has an advanced knowledge of the strike zone and solid pitch recognition skills. He still will get caught out in front on breaking pitches, especially early in the count as he aggressively hunts fastballs. With two strikes, however, he will shorten up and has no problem taking what the pitcher gives him.
To compliment his potential plus hit tool, Devers also has plus-plus raw power and the potential to hit for plus in-game power. Devers’ swing isn’t the typical, left-handed, power hitter uppercut with a high finish, but when he catches the ball right he can lift the ball and drive it.
If you see him play the field, it’s clear that there is no reason to discuss a move off third base at this point. Perhaps, he could eventually become too big, similar to what happened to Miguel Cabrera, but his skills should allow him to stick at third for the foreseeable future.
It is telling that given how many top prospects the Red Sox have traded since Dave Dombrowski took over, the two offensive blue chippers they held onto were Andrew Benintendi and Devers... But despite the growing drumbeat from fans to replace Sandoval, Devers is unlikely to be ready to take over the position this season (although, given Dombrowski’s track record, I wouldn’t rule out seeing him at the big league level later this season if the third bases situation is still unsettled).