AFAIK Prestige used to manufacture hulls for Ribeye but went bankrupt and then Ribeye bought them out. They are certainly very similar RIBs to Ribeye right down to the Ocke Mannerfelt designed stepped hull. I would say there is very little to choose between them, even the tubes look identically made with different manufacturers logos.
As regards build quality IMHO if it is a major concern for you then I would agree with Tim and stick with a Tornado or any other UK manufactured RIB for that matter. Have heard too many bad stories about SA manufactured RIBs and simply would not take the risk!!
If it is the price that attracts you to them, there are still plenty of better cheap Ribs to be had in the UK:
being the first two that spring to mind.