They're already in field use, and are apparently fine at it. They just do big, straight wall stretches for things like hospitals. The "would lose to master masons who have to put up corners in a speed contest" metric is a bit silly - on non-corner work they're operating 3x as fast as the masons they're alongside. No real risk they're replacing humans, but they do work.
Since they replaced journeyman masons there will be no new master masons and once all the master masons are dead they'll have to do that corner work too.
Fortunately, they don't seem to have replaced journeyman masons either. Journeymen still do corners and other complex features, they just do it with oversight. Rather, there's a shortage of masons at all skill levels, and so far SAM is only cost-effective as a way to help fill that gap on very large projects.
I'm sure that will change with time regardless, but I don't think it'll be because SAM drove out human expertise.
It appears to be a standard 6 axis robot arm equipped with a specialist end effector designed to pick, mortar, and place bricks. It's possibly on a linear track to drive up and down the wall too. This is likely far cheaper than designing and building a specialist robot for this one task.
https://www.technologyreview.com/s/540916/robots-lay-three-t...