Surely that depends on what you think it does?

As it would appear the HRC and Mmax ones do both wire splices they do effectively advance the timing over what it would be without the box in place so whoever told Dave it "advanced the timing" didn't lie, they were just a little economical with the facts.

The point is it says HRC on, there is always going to be someone who will pay over the odds for it, the NS30 ones that do nothing at all except remove the top end speed restriction (a task which can be accomplished with a 15p resistor) go for £150+ on fleabay.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread