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Here's another pic of my genuine BBS Monza 18 before powdercoating - In other words, diamond-cut and with grey inserts:
^ The most obvious difference is the amount of alloy between the 5 'holes' and the tyre at the rim. I now feel pretty sure that the one you are asking about is a replica. Hopefully it's not being claimed to be genuine. I don't know how the Ronal design differs, if it does at all - I would not expect it to differ as it's an OEM product.
BBS developed their patented 'hollow technology' on the Mk5 GTI's Monza wheels, so a genuine BBS/Ronal is probably lighterweight than a replica. Monza 18's are 11 kg (to the nearest kg).