That's old tech Neil.
Continuously laid concrete - i.e. without joints ! - has been around for over 25 years.
It stays remarkably smooth - well, at least in our moderate climate.
We have a stretch of road here, laid in the late 1980s, that'd still be baby-bottom smooth if it wasn't for the road authority's desire to cut holes in it !
The stretch that was laid a few years ago, is nowhere near this quality however
Old style concrete plates do shift - up and down - likely because they lack the sheer weight and the resistance to movement of a continuous slab.