

We will know in 30 years if they are really cheaper over their lifetime.
France did a similar low cost mass production of nuclear reactors in the 1970ties and those reactors turned out to have a lot of construction defects some decades later and costly repairs really drove up their total costs.
I believe the bigger issue is that once you have started them, a lot of the interior is radioactive (even when turned off) and thus repairs become quite complicated, compared to doing a more thorough job during construction when there is no radiation yet.