They’d be f***ing disappointed. They thought we’d be a century ahead of where we actually are.
Where, they would demand, are you hiding the fusion-powered flying cars? Where are my pocket transmuters? You can’t seriously mean that people drive to work instead of teleporting? And what about the Mars colonies? You mean you don’t have any?
Supermarket scanners would probably seem cool to them, but the principle was known from 1952. It just took until the 60s before they could build a maser that worked with light (and another 20 years before anyone thought of anything useful to do with it outside research; it was described as “a solution looking for a problem”).
Seriously, most of the technology we have today is built on science from the 40s and 50s. They’d have huge problems duplicating it, because the manufacturing capabilities weren’t there. They couldn’t build machines to the precision required for a manufacturing plant for modern computers. They’d need to stuff a smartphone into an electron microscope to see the details of how the processor worked, and they’d marvel at the miniaturisation.
But they would have no problem at all understanding it.