Can you post a link ? I checked Copes and could not find them. IF they are Bulgarian origin for that price they are likely the commercial made non-lined smooth side polymere Those are OK range mags but the all plastic lugs actually break off when bumped around.
They are commercial. Made by ISD, or whatever name they go by now. I owned one of the earlier models of this mag and it was a fine range-unit. I would go with something reinforced if your life depends on it though. In any case Copes is a good outfit to deal with.