HRC are just as guilty, you should see what people pay for the HRC ones for the 400's, as far as I'm aware all the "plugs inline with the normal wiring" stuff do nothing that can't be achieved for pence, only real HRC/F3 replacement CDI's are worth bothering with.

Click here for an finished Ebay auction for a resistor in a box with HRC written on it.
Yes, that is nearly £200 for absolutely nothing, the "alter the ignition curve" bit is an urban myth

As for the '21 HRC box, my £££ is on it being nothing but a tidy wiresplice (hence someone worked out the wire splice by taking one to bits ).

But the best clue as to it doing nothing is that quite possibly the most powerful normal road going std NSR250 engined '21 in the country (Andy's) doens't have one
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Please do not PM me technical questions, if you can't find it on the Forum start a thread