Not had personal experience on the HR as I don't have one, however I have sold a few sets and received good feedback. I doubt they are any different to mine really.
My own personal opinion is a stock Zed is very quiet, it needs an aftermarket exhaust, no doubt about it. Then if your like me then you want to enhance that too, the HFCs do that perfectly. I'm sure they are not to everyones taste. I'm sure my neighbours are not keen on them either
Personally as a 350z owner 'and not because I sell them' I think they are a must