There are 2 schools of thought regarding reproduction parts....all depends what you want to use the bike for.
If it is a show build then repro parts are a no no. If you are riding the bike and don't want to destroy rare old parts then repops are the way forward. Most people us a combination of both.
Some repop parts are rubbish and just look like the original, some are better having been made form 80's moulds/ tooling,,,there will usually be some sort of distinguishing markings or date stamps etc that will differentiate from the original part to stop people passing them off as originals but that does not stop some people!