I have both, gave my son the pro 18 two or so tears ago after hacking it. Sent my pro 668 to whistler for the official upgrade after I hacked it. My son just brought the pro 18 back to me and I loaded the same scan list to it as my now whistler upgraded pro 668. I here twice as much on the 18 as I do the 668 and simulcast is very slight compared to the 668. Was the hardware better or the firmware?