I think I found the answer.
This is what the details of the RR shields say.
This pack includes 60 shields. This separate pack will allow you to carry out conversions or replace metal shields with plastic shields. The shields are designed to go with the Victrix range of LBMS Roman and Carthaginian shield transfers.
Ordered them a few minutes ago. Together with some Iberian Cavalry and Balearic Slingers, the only ones still missing from my Carthaginian army.