Great move by the Giants, as long as Devers isn't dead set on playing 3B on a regular basis with Matt Chapman and his vastly superior glove ensconced there.
The Giants needed more hitting and had a surplus of pitching to deal from. I still have hope for Harrison figuring it out at the big league level, but I don't see him becoming Zack Wheeler 2.0 by this point.
Devers is on a big, long term contract, but he's still fairly young and the market has only gone up for elite hitters since he signed. His bat will play at Oracle — he's got power to all fields.